I think mobile AA needs some work, even Jethros, which are arguably the best mobile AA with their speed, power and utility, seem to sometimes lose vs bombers, and many of the other AA is weaker. Things like speed, range and HP are not necessarily a direct exchange for DPS/cost because it's DPS/cost which actually stops the bombers, and if you don't have enough of this, you aren't cost efficient.
All mobile AA has a kind of role, Tarantulas are great mid and late game at hiding on hills and sniping air, Flak has AoE, Crasher is fast. But the use-case for 1v1 is almost always: Can it effectively kill Shadows. If you can't do that, you are much weaker to air starts or switches in a 1v1.
I'd also consider some secondary utility, like radar on the Crasher, shields on the Vandal, etc.
Frankly I prefer static to mobile AA, creating a domain where bombers must pay a cost to enter, where this communication between air player and ground player is clear, unlike, say, Jethro's, where it's just 'Surprise! You lose all your bombers!'. But the only practical AA to build early is defender spam (ugh) or Razors Kiss (Which is really hardened AA, and does not create a land-snipable point of failure). Flak and Chainsaw are too expensive to fit in this gap, and Hacksaw is owled, so we keep using rkiss.
But anyway, air is
GoogleFrog's domain.