Pop cap means you can't build a numerically superior force thus the game only rewards armies that can build higher quality units.
Please explain why UKF is not strongest faction in the whole game then.
Pop cap means better planned army that is adapted to countering what opponent does wins.
Axis will always beat a soviet player in the long game, not because they are better, but because they can build panthers at a better pop density than soviets can build t-34 76s. No skill is involved in this. Just arbitrary numbers.
This is why soviets don't spam T34s, but support them with SU-85 and ZIS guns that keep panthers well in check as well as katiusha that helps break impassable HMG+atg and axis infantry walls.
Planning your army and anticipating future units is part of skill.
If you are spamming a unit against a unit that beats it, its not "arbitrary numbers" its you being an utter scrub who couldn't adapt to situation and tries to blame everything but himself on the loss.
If you are spamming grens vs USF with expectation of winning on the long run, you're bad and balance has nothing to do with it.