Just wanted to start a discussion on the perception of balance where the difficulty of a faction is the driving force for common views on how each unit performs.
From my browsing on this forum and the COH2 subreddit, I think a fairly common sentiment is that both axis factions (more so Ost, but OKW is not far behind, at least as game modes get larger) are fairly braindead to play atm. The overall design of these factions, in addition to unit philosophy and performance is what makes this seem like a fact. At the core of it, it's a lot easier to micro one very powreful unit (axis) than several weak units (allies). Additionally, axis is generally more forgiving now when it comes to losing units, since they have many backup tools that can help them stall back into the game.
When it comes to performance/cost, I don't think any faction is significantly more "OP" than another, but I think the reality of how immune a faction is to fuckups is what shapes perceptions of balance.
I think rather than discuss how to avoid making units OP, for COH3 we need to equally discuss how to make each faction relatively similar in simplicity of play, and not the huge gap like there is between axis and allies in both coh1 and 2.
The simplicity of play is a minor issue imo and trying to achieve will probably lead is making faction too similar and the game feel more like Age of empires than anything else.
When it comes to team games thing become more complicated since synergy between factions becomes an issue.
Generally speaking Axis faction have good synergy since OKW are good at early aggression while Ostheer are good at defending.
When someone designs factions one should also consider how something will effect team games. For instance the UKF M3 resupply HT was not really an issue for UKF player or UKF teams but it did become an issues when other factions become part of the team and especially Soviet. There were solution around but the would require creating a unified system when it comes to slot weapons that was simply not there.