But you are basing you statement on the idea that each attempt ever should be solely based and determined by that players' attack force. Which, pardon me saying it, sounds very 1v1-focus biased and not representative of team games. Like in 1v1 there is no one else to cover for you, so I understand your sentiment of "if you can not do it yourself, it means you can not do it at all, which in turn means you are losing by doing it", but I think it's realistic to leverage additional support from one of your teammates if he is ahead enough to afford it - like, for example, from your sheltered air player - where most of the "air T3 rush is oppressive" sentiment arises from in the first place - because someone can afford to do nothing but rush for T3 air.
Following your reasoning, you shouldn't push ever if your army isn't overwhelmingly stronger, which means that in an ideal game, you will never push, and solely rely on using your ground army as a deterrent. Which isn't unreasonable, but it means you assume any and all games should be ended by sniping the ACU despite all of the infrastructure and units it has supporting it. Which is cost effective if you can pull it off, ofc, but I don't think should be the pivoting point of the discussion.
Tenderizing your ally's push path seems quite a reasonable strategy to me - either by doing it directly, say bombing the enemy forward combat units, or doing it less directly, by bombing their eco (say to stall enemy E, so shields go down, or their factories, to reduce their unit output) or other fortified positions - it won't take ages for a couple of T2 bombers to take down a couple of T2 shields. And yes, you might get the enemy to react by building disproportionate AA to dissuade this, but then you achieved your goal - making it easier for your ally to push (given some BP and mass was invested in additional AA by the enemy, instead of ground-striking units).