I find unnecessary to reduce the number of slot to 1 for all infatry.
On the other hand, imo normalizing and simplifying game mechanics is a much better investment of resources than over buffing and then over nerfing units/commanders/abilities which seems to be the pattern with COH2's patches.
The pattern with nearly every online multiplayer game in existence* (my point here is that's kind of just how balance tends to work with these kinds of games, up to opinion on whether given units were overnerfed/buffed at the end though)
(Edit: just realized you said UNnecessary, so imagine the next paragraph reworded with "mechanics" instead of strictly "weapons." And also take the last two paragraphs as not necessarily directed towards you then)
Also, the two aren't mutually exclusive. In fact, normalizing weapon slots would likely involve (over/under) buffing a bunch of weapons, then subsequently (over/under) nerfing them. No real point here, just a comment.
Finally, the existence of multiple weapon slots makes the game more interesting, even if it can lead to imbalance in certain situations. Axis vs allies would no longer be a 1 weapon vs 2 weapon dynamic (higher cost, lower efficiency, but more potential) and would probably be a "whose upgrade is better" dynamic. Of course you could make try to make the dynamic more interesting by further differentiating the profiles, but im not sure how far you can take that idea before you have to essentially create clone weapons. You could also adjust the number of weapons given per slot, which sounds workable, but I still don't like how it separates upgrades into singular spikes instead of the tiered ones that multiple weapon slots provide.
As with a lot of things, this is a matter where the specifics (the numbers and the actual hard implementation) would probably be more important than the concept alone.