Imo it depends on how u define the term teamplay. If teamplay for u is you and your teamm8 being present all around the map (the VonSildur/HooliMan god mode style) it would kick in only top 30. But i think teamplay is already there if you got your tank at the right moment there to help your teamm8 out, or you got your units on the spot where the enemy is about to flank. Or when u do a single combined push on one of your opponents.
For example i played with a friend of mine against wuff and some other guy yesterday, me and my friend were both struggling until i shifted to the side of my friend as well (and forgo our fuel point) to help him destroy a sovjet stronghold. we completely demolished my friends opponent (together), which allowed us to get back in to the game. These kinda actions were you play together qualify as teamplay too imo.
so since i am not top 30 i disagree with the statement that teamplay only kicks in the crême de la crême of the ladder. My point is that teamplay is important and also can be a crucial factor on lower levels. (it might not be the godmode teamplay of the guys i named ealier but it is still teamplay and will win u games if u work together on the right moment)
TEAMPLAY MATTERS!
Oh it's certainly usefull, but AT already implies a level of coordination (picking suitable factions) and working from there. True teamplay is communcations, similair pushing and coordination strategy and attacks, all of which is not needed untill said top 30 (heck, the best 2vs2 team every, asten and jove, never so much as spoke to eachother and they are still kicked ass, so even in top level it's not as needed).
What is needed in 2vs2 (AT) is a. rushing the house b. winning the arty war.
Get that down and you don't need teamplay 95% of the time.
So in a sense, we agree I think, just disagree on definition and necessity.