Like FTX said, T2 already is OP and increasing the T3 air HQ cost+time just makes it even more OP.
There are three scenarios.
No specific airspot -> If your opponent goes t3 air and fucks your team, then it's your fault by just not pressuring him aka allowing that huge investment.
Map has an airspot and air have equal rank/skill -> Air is balanced and shouldn't deal much damage
Map has an airspot and air have unequal rank/skill -> The high rank has to either crush his opponent fast enough or basically just cancer the enemy airplayer. That's totally doable in the ~11min timespan (high ranked games <10min).
Take this as an example.
#18316776
The enemy airplayer (2000 global) was stronger than my airplayer (1600-1700). Since I was the high rank and on the front spot, losing the game is 100% my fault by just playing insanely bad (which I won't deny at this point). This is a scenario where I should've either went for more spam early on to just crush my opponent faster or to rush a TML/artydrop/Corsairs to cancer the enemy airplayer.
Since t3 air rush is pretty simple overall, the timing of t3 air doesn't allow a huge gap if the ranks are different. (I'd say 200-300 rank difference is the point where it gets abuseable)