Imo the biggest problems of Ost is that they don't have infantry that can decently trade with elite Allied infantry and on to of that being a little bit squishy. For example OKW have obers and having 5 men mainline infantry also helps a bit.
Pgrens are quite awkward and only good vs stock infantry and guards in cqc or with psheks (not mentioning infantry AT being rng cannons). I quite like g43 upgrade on them tho.
With all being said I think it is the most fun faction in the game.
Ost is supposed to use 251, HMG and snipers to win infantry engagements.
You aren't going to be winning with cheapest mainline infantry with cheapest upgrades in game.