They absolutely should converge past a certain point.
In a perfect world, all factions should have the same 'strength' at all points of the game, only the source of this 'strength' should be different for every army.
In a perfect world, there would be a reasonable number of situations in which, for example, you want to build a Soviet scout car or an OKW puma at minute 50.
In a perfect world, every unit would scale well into the late game (through some combination of power, survivability and utility), and there would be no light vehicles with an expiration date.
But even in this real world, an indefinitely long game should be decided by skill. 'Army X is OP lategame but it sucks in the mid-game' is an example of two problems that don't cancel each other out.
I think the original source of this 'early-late' assumption is the per-unit superiority of Wehrmacht armor in vCoH (which, in turn, was doubtlessly inspired by someone's Krupp steel fetish). US were (or should've been) designed to counter it with numbers, coordination and veterancy. But since this balance tended to work past a certain skill level, if at all, the myth was born.
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Muad'Dib
Relic Entertainment
