As a cheap unit with extremely powerful AA capabilities, the Aeon Restorer can be a very difficult unit to counter. It costs twice the mass / energy of a Restorer to use other gunships as a counter, and ASFs also prove to be difficult to use effectively. Ground-to-air flak is effective since the Restorer has weak ground weapons, but of course, it is relatively easy for Restorers to escape, or use their high health to destroy the ground based AA before flying away to repair and refuel.
The best counter is, believe it or not, Interceptors. You should try it for yourself if you find it hard to believe; this was discovered under heavy testing and analysis. If you use Interceptors as a counter, you save a lot of resources mass-wise (and it costs a lot of mass to make a Restorer); it costs a little bit more energy, but it saves you much more energy than you would usually spend using other counters.
With that said, this is not to be taken lightly. Using interceptors as a proper counter requires micro-management and constantly keeping an eye on your opponent, but the results are worth it if your opponent is constantly spamming Restorers.
In early stages, it takes 13 interceptors to take down an AA gunship. Testing shows that the ratio decreases (with proper micro-management) if you are forced to face around 20-50 AA gunships, but you should still keep the ratio at 1:13 to be on the safe side.
In terms of micromanagement, when you feel you have enough interceptors to take out AA gunships, or when the time comes to attack them immediately to defend yourself, you need to divide your inteceptors into groups, about 20-100 interceptors per group. Make sure that they will all arrive at the gunship fleet at the same time, and also assign each group several gunships: try to make them attack different gunships, but if you accidentally, or are forced to, assign a gunship to 2 different groups, this will not make much of a difference.
As you see the number of gunships decreasing, be sure to continue micromanaging, since interceptors swoop in, turn around, and fire again. If you see some interceptors outside the group getting ready to fire again, it doesn't matter how many different groups the interceptors are in: select these interceptors, and have them attack the most likely target they will hit. This will require practice, but you will find you have a large amount of interceptors left over.
As was previously stated, this strategy cannot be done lightly, even though it proves to be an asset. You are going to need Air Staging Facilities to refuel all these interceptors, and on water maps, a carefully-guarded aircraft carrier is a plus. You also need to be aware of what your opponent is doing to counter these interceptors and be ready to fight back, remembering that you and your opponent will still be spending the same amount of resources trying to counter each other (which means you will not be put at a disadvantage assuming your resources are doing well). Here's a few examples:
- Your opponent may be making ASFs to take out the interceptors. Make your own, and send them with the interceptors. Micromanagement is extremely important at this point, you want your interceptors to attack the gunships, not the opposing air-superiority fighters.
- If the Aeon player is sending flak or Cruisers (especially Seraphim Cruisers) to escort the Restorers, build up a naval fleet. Submarines and cruisers will do a lot to take out these escorts, plus the Restorers at the same time. If your opponent is escorting his AA gunships with naval, chances are he's either going to stay there and allow your naval AA to pick him off, or he's going to flee and thus allow your interceptors to attack safely.
- Your opponent may have a lot of Anti-Air inside their main base. That's quite all right, if he's keeping his AA gunships protected there, he's not sending them out to attack you and so you don't have much to worry about. Don't make the mistake of trying to attack his AA gunships in a well defended base, your interceptors will not last long.
In the end, if you're not willing to put in the micromanagement required, spam some ASFs to take out AA gunships, this proves to be effective. But you require 2 at least ASFs for every Aeon Restorer, so you are spending a lot of energy.
The only other thing worth mentioning is, if your opponent is going to keep spamming Restorers throughout the game, don't get obsessed with interceptors: they do their job, but they prove to be an inconvenience after a period of time. While you use your interceptors to counter, you should build up defences (like flak, cruisers, SAM launchers and mobile AA) as if there was no such thing as an interceptor. Eventually your will reach the point where you don't need interceptors any more, as spamming Restorers will become an ineffective and useless strategy for your opponent for the rest of the game.
T3 Air Superiority Fighters require far less micro-management, but are typically less effective at countering Restorers. The extra speed they have normally as an asset often means that while they are turning around to fire at the Restorer, they cannot fire at it, but the Restorer's AA Missiles will track in all directions, effectively turning the speed into a downside. While purely on a statistical level, you should only need two ASFs to take down a Restorer, often you need three or more if they are not Cybran. Three ASFs equal the price of a Restorer in mass, but cost three times the energy, meaning that this is actually often not cost effective. To maximise cost-effectiveness, it is often best to get the ASFs to turn around outside of the range of the Restorers and to attack in as great a number as you can, minimising the time that the Restorers can fire back at the ASFs. Since ASFs are faster, they can run from Restorers if needs be, ideally to refuel and rearm, but potentially to get away from other air support - if an opponent has split their air superiority between ASFs and Restorers, you could easily draw their ASFs away and fight them separately, splitting up their air power in a "divide and conquer" strategy. As a Restorer vastly outranges an ASF, it's best to attempt to draw it away from anywhere it may get radar coverage as help (as radar greatly boosts a Restorer's fighting ability). In a prolonged battle between ASFs and Restorers, it typically comes down to who has the best support units (units on the ground/sea etc).
Please note however that Cybran Geminis, unlike other ASFs, will defeat a Restorer cost-effectively using their missiles.
While Aeon can counter with their own Restorers, a cost-effective way of killing Restorers may very well be their combat fighters. Far, far more efficient than other factions' Fighter/Bombers. To equal the cost of a Restorer, you would need six Combat Fighters for mass and just under four for energy, so rounding that to five to be approximately equal, five combat fighters have nearly six times the DPS about 6/10th the health. That does mean that Combat Fighters will often be able to deal a lot of damage Restorers quickly, and while they die and their overall damage goes down, they should be able to combat Restorers a little more effectively than ASFs when used in overwhelming numbers. Ideally this does mean that you use approximately 5-6 per Restorer, and should have some left over after you are done. Flying faster and with far more health, they are somewhat less vulnerable to ground-based flak than interceptors, but that does not mean that they should be left in areas of it for extended periods of time. Their high speed makes them an easier counter to use than Interceptors, as they can easily get around the map quicker, helping to defend a base under attack by Restorers.
Ground defences are key to defeating Restorers efficiently. While ground defences without air support will usually get chewed through due to the Restorer's large amount of health, a good defence outpost (with several shields, an air staging platform and even a small amount of ground-based flak and perhaps even just one SAM) can easily turn an air battle from a defeat into a victory. Shields are usually essential, and often overlapping shields will help allow a shield to come back up instead of the Restorers focusing on it and destroying it after they take it down. For instance, it will take about 5-6 Restorers to get through two overlapping T2 shields (that are not Cybran), as any less than this will simply mean that the first shield will come back up before the second shield goes down.
When actually building anti-air to support your air force, try and mix T2 Flak with T3 SAMs. T1 anti-air is not actually a bad choice when fighting Restorers, but since it's largely inferior to Flak when fighting multiple aircraft (especially when you factor in the flak's extra health) it's generally a better policy to build a single T2 flak installation than multiple T1 Anti-air turrets. While SAMs offer a lower DPS per mass, they do allow for engaging Restorers are a much greater range, meaning that if they decide to flee, you will often take down several as they run away, and it also means that you don't have to "drag" an air battle too far to get it in range of your ground support units.
When fighting over water, the presence of Cruisers can be instrumental in defeating Restorers, as their high amount of AA-DPS can easily turn battles, but a smart player using Restorers will either try and run away to draw the fight away from the Cruisers, or will try and deal with the Cruisers first before moving onto the rest of a fleet. This means that shields (if available) for your Cruiser are greatly helpful. Similarly, the Restorer player may very well bring a fleet of their own to counter yours, perhaps including Cruisers of their own. If so, it would of course be a gameplay decision on what to do - whether withdraw your air force until you've defeated their cruisers, or perhaps bring in your own gunships to kill their cruisers quicker, etc etc. The main thing to be aware of is the effectiveness of cruisers and how their presence shapes an air battle.