You seriously overstate of how much combined arms in coh 1 there actually was.
Were ranger, airborne blobs "combined arms"?
Was zombie grenspam "combined arms"?
Was sniper spam that was super annoying and also you saw it in pretty much all games ever "combined arms"?
Sorry, but coh 1 also had a very shitty metagame throughout most of its life.
At a high level CoH1's meta was really never like this, because in CoH1 homogenous unit groups are a lot easier to beat than combined arms. Sure, there were situations where single-unit spam was the best option in CoH1 (funny enough it was situations that mostly involved the OF factions), but if you went into a game against a good player with the mindset that you were going to primarily build one unit and one unit only, you were going to have a very hard time winning.
The thing with strategies that involve single-unit spam is they're generally relatively easy to execute but relatively difficult to defeat. They're also extremely inflexible. And once you get to a level where your opponents know how to play against them, they're very hard to win with because they don't give you many options. I can't speak to CoH2, but that's how it was in CoH1.
As for the OP, I agree with a lot of the comments, but I don't necessarily agree with the conclusion. I don't think it's really ever been a balance problem, but more a design problem. The vanilla matchup in CoH1 wasn't always balanced, but people always loved playing it because it was designed in a way that encouraged active and dynamic gameplay. It combined tactical and strategic decision-making in a very unique way. Ever subsequent faction design in Company of Heroes has strayed from the model of the core factions, and they've suffered as a result in my opinion.