I was conceptualizing units for a laser weapons oriented faction, and was thinking how I could make their ASFs unique, and one idea I had is an ASF with omni-directional fire (or at least being able to fire from front and back), but ofc with reduced DPS to compensate.
One other method of adding flavour to ASF is to add a bit of diversity to their weapons. I don't think you can make it work by changing their speed or health dramatically, but weapons could work. One example of that is above - omni directional weapons.
For another example, you could give Cybran ASFs double or even triple range, at the cost of DPS - they fire missiles, might as well make them fly a bit further. Aeon could get some AOE. UEF could get flares, so anti-air missiles aren't as effective or something.
I mean you could always play with movement speed, acceleration and maneuverability, but that seems like a lot of 4th digit adjustments for a long period of time - not that the aforementioned weapon changes would be easy, but at least they feel somewhat inspired.
Anyways, these kinds of changes would mean you'd approach different ASF fights differently depending on the faction you are playing, which I'd argue is the core 'problem' the now-presumably-inactive OP actually had - every faction was the same, and there was no dynamics to the air game - just get to T3 asap, and then spam the living hell out of ASFs.
I mean the problem is not only with the ASFs, the only 'outliers' in the whole air lineup is the Mercy, given it's quite unique only to the Aeon - everything else is somewhat present in all/most factions. Which ofc you need so one faction is not inherently stronger, but it kinda feels ASFs are that much more bland. Like the biggest diversity in units characteristics are T1 and T2 bombers, but again they are not viable the moment T3 hits the game (which is usually rushed, so useful for a very short time).