Why is everyone opposed to a multi-role fighter? typically they aren't superior at either and are quite functional; in fact it is IMO what the air-game is missing, otherwise its fighter->better fighter and a bomber which is kinda lame. In supcom2 they were the difference in factional air-forces, the side that had only specialists (which were actually weaker but never distracted)had generally better air-superiorty; in a faction-less game there is no argument against this sort of unit besides subjective things as 'I don't wanna.' Edit: they also existed (shock/horror) in Total Annihilation (could shoot missiles at the ground).
And that is why they do not exist in SCFA or PA. Hawk swarms were the only viable option in larger games, and massively overpowered. FA still has problems with mass air in big games, and PA does too but perhaps to a slightly lesser degree. Balancing air in these games is incredibly difficult. When GPG abandoned Forged Alliance, they left it with the Restorer the go-to strategy, it was a gunship with massive AA ability and pretty good anti-ground abilities, and it was unstoppable in large numbers. Air is already fast enough to run away, also give it the ability to hit any target at all and it's a recipe for disaster.
Depending on cost, damage, among other things. I can make one that can target literally any unit in the game and still make it Underpowered. Want to watch? I can save us all the trouble and tell you I would give it 80 range and 10 damage a second for 800 metal...
You missed the point entirely, and heres why -- a big mindset, let me dispel it; There is a massive difference between a multi-role fighter as they exist in RL, TA and SC2 and a beefy gunship with AA to boot! For starters a multi-role fighter fights with missiles, which are generally a low ROF weapon, and for two they are easier to kill, and more vulnerable to air superiority fighters and other forms of AA (including ground AA) and use fighter approach maneuvers making them poor at anything other than alpha striking.
Yeah everybody let's have an even faster dox that can fly to other planets! What could possibly go wrong?
I would argue that it is impossible to balance an air unit that can target anything. Either it's so good there's no reason to use anything else, or so bad you'd never use it in the first place. Using FA as an example, three factions have a T3 gunship. UEF and Cybran have around 230dps each, but the Aeon one which also has good AA has only 120 ground dps. Aeon Restorer also has reduced speed as another means to weaken it. All three have comparable price and health. The UEF or Cybran ones have a specific role - they can do serious damage to ground target if you are able to protect them from anti-air, primarily by using fighter planes. By comparison, the Restorer is capable of defending itself to a degree. If it is set powerful enough that it can actually defend itself entirely, it becomes an unstoppable assault weapon. If its AA capabilities are not enough to defend itself then it requires fighter support in addition to reduced speed and DPS, and is clearly a worse choice than the other factions' T3 gunship, and even a worse choice than the same faction's T2 gunship.
That is unless you heavily nerf it's ground weapon- but then at some point it might as well not even have a ground weapon.