T3 alone isn't too powerful, it's T3 backed up with T2 which is too good to pass up in favor of T1-T3/T1-T4/T1-T2-T4.
Grenspam even got slightly better now that sniper spam has been nerfed a bit: all you really need is vetted inf and a single countersniper. It's hard to beat as US if you lack rifle vet (i.e. you went fast m8).
Agreed.
I disagree with the suggested volknerfs aswell. The Tier1 phase is pretty balanced right now, with lowered upkeep and reinforce costs for riflemen. The reason US starts to be pushed back later is partly because of this lack of rifle vet. Increasing the veterancy award rifles get from killing volks (not from any other units/lowering their overall vet requirements!) might be a nice tweak.