We have three primary Air Experimentals. The weakness of them is the ASF, as it should be, but one is definitely more equal than the other two. Since none of them are threatened by any but the most concentrated AA, and have enough DPS to level medium-strong defenses anyway, survivability is limited to the ASF encounter.
Soulripper - Always seems to do the most. Seems to be worth building. Mass - 34,000. HP - 90,000. HP/Mass - 2.65
Ahwassa - Next most useful. Incredibly front-loaded, so unless air control is seriously against you, it will usually do something, even if it dies immediately. Levels T3 AA in one pass, so with Air control is a true game-ender against all but the strongest ground defenses. Mass - 48,000. HP - 52,000. HP/Mass - 1.1
Czar - Almost exclusively referred to as a suicide donut, to the point it's become a running joke. Rarely does work. Requires time hovering over its target tanking fire to do anything, similar to the Soulripper. Does not have advantages of frontloadedness, seriously high AOE, or high speed from the Ahwassa. Mass - 45,000. HP - 58,000. HP/Mass - 1.3
So... The Ahwassa, now that the arguably-exploity bombing of ASFs is gone (Don't argue that here, it's not what this thread is about, and is besides the point), the unit is probably just about usable. Soulripper, too, is just about usable. It has the HP to tank while it deals its damage.
Czar requires time to do damage, like the Soulripper, yet has only the survivability of the Ahwassa. No wonder it's so delicate.
Observation: Despite recent nerfs, T3 Bombers still considered too strong (I think) against T3 AA.
Observation: Despite recent nerfs, ASF spam is still as important and sweeping as ever. Still considered a gameplay failing?
Possible solution to Czar problem, and to a smaller extent, Ahwassa and Soulripper: Buff HP. In the Czar's case it would have to be significant.
Usual counterargument: With buffed HP, how would you ever stop them with AA and not ASF. You'd never be able to without a ridiculous investment of mass and space!
Counterproposal: Significantly buff T3 AA DPS, slightly buff missile-based solutions' MuzzleVelocity and/or missile velocity.
Problem: But that would ruin Air and make attacking bases impossible!
Would it? It would shoot down ASFs even more handily. Doesn't seem like it would be a huge problem, the numbers involved shrug off even hefty AA fire in the short time required to have the fights. You'd have to be more careful of where you engage, sure, but the ASF role of clearing out air-to-ground threats would be undiminished. Even stopping an enemy Air Experimental in their own airspace on the defensive will still be accomplished in one pass.
T3 Bombers are still going to drop their bombs and die. This interaction seems unchanged for the most part, except that forward-placed AA might work now.
Experimentals will be defendable. It will still take a hefty investment, as it should to stop 30-50 thousand mass invested against you, but it will be doable, and those units might get there more reliable, and be used more.
Spy planes would be caught properly by T3 AA.
TL:DR
Experimental Air seems less used because of how delicate it is against ASF (Crucially, how even if you have a far superior ASF force of your own, the enemy can still suicide a smaller number of their own against your Experimental and kill it in one pass before you physically have enough time to kill all their planes), and how countering that with more HP would make T3 AA unable to stop it. Upping both would leave the AA vs Experimental Air relationship as-is (ish), make the Experimentals more usable, and have negligible effect on the rest of the theater.
Czar - Boost to 94,500 HP for HP/Mass - 2.1
Ahwassa - Boost to 62,000 HP for HP/Mass - 1.3
Soulripper - Seems OK as-is.
T3 AA - Buff from 333 to 530 DPS. Missile variants +15% Missile velocity.