That's the thing though, it seems like they're buffing all SMGs to match the Carb. Even if you buff ARs the SMGs will most likely be able to overpower them in short to mid distance, it kinda comes down to the way the maps are designed, 80% of the time I don't think I'd want to use anything other than a SMG. This is of course partially because no one else uses anything other than SMGs, but I feel like most maps cater more towards the ranges in which an SMG is effective. If the only trump card the medium has is the ARs that's not really a good deal IMO, especially since a heavy can use them as well with a lot more health to boot. Limiting ARs for heavies wouldn't work either since logically you'd have to limit SMGs as well. They're supposed to be a happy medium but I just can't see the appeal.
I'm really curious to see how they'll go about it!