Pgrens should go back to t2, and no they won't become irrelevant. Are you under the impression they got no other buffs when they were moved...?
The buff they got are:
"Population from 9 to 8
Infantry Doctrine Combined Arms now a veterancy 1 passive. Med-kits veterancy ability removed
Combined Arms ability now triggers when near allied vehicles.
Veterancy 2 now adds +16.7% weapon accuracy.
Veterancy 3 accuracy bonus from +40% to +20%; total accuracy value increase at veterancy 3 remains as the same as in live.
Reinforce time from 8.5 to 7.
Build time from 34 to 28."
Now if you think that this is enough to make PGs as 5 unit build significantly more viable I doubt it.