I'd assume it's because having PGrens in T0 enables skipping T2. That gives you extra 200 MP to play with now and your rushed T3 unit 20 FU earlier.
With benefits like that, it's hard to argue in favour of building T2 unless you desperately need a unit from it.
Regardless of whether or not the Ostwind rush needs tuning, some of T2's cost ought to go to BP1 or BP2. T2 just isn't very cost effective right now.
Could build a sniper and watch that 200mp bleed away if they are relying heavily on pgrens.
As has been said the meta is shaken and players need to try new things rather than the same things and complaining they don't work. We have at least another week before we can truly tell what's properly "op" and players just havnt figured out how to deal with yet