Makes perfect sense really.
Rifles need to be aimed, you don't just mash trigger because gun allows you to.
Carbines and garands aren't really all that different in CoH games.
Aiming is fairly intuitive at the distance which this game considers "close range".. In fact, I would even go so far as to say that when you're 5 meters away from someone, fine aim is way less important than being the first one to fire a shot (and keep firing until the other person can't). That's where the whole "semi-automatic" thing starts to shine.
Now, I didn't come here to have a discussion on balance. I was just agreeing with the OP (for flavor's sake, at the very least) that carbines and bolt actions having a comparable RPM at close range is kind of silly. Even if DAK panzergrens are supposed to be some kind of Über-elite supersoldaten hopped up on panzershokolade, they still have to contend with the fact that the magazines on their K98's are three times smaller than that of the M1, and yet again, they have to manually cycle the action after every shot. And you're telling me on top of all that, they have to really carefully pick out all their shots for some reason? Either the DAK panzergrens are working their guns like madmen and not aiming (so that thir rate of fire is even remotely close to that of the M1), or they're taking their time and aiming while the paratroopers are languidly firing their carbines like they're just having a fun day at the range. Either way it's silly.
So no, I very much disagree that it makes "perfect sense". What would make sense is if the panzergrens fired their rifles slower at close range. Easy peasy. Whatever you have to do to make the DPS the same as before, do it. Again, I'm just looking at this from an aesthetics standpoint; it does not make sense that in close quarters combat, the paratroopers and panzergrens are firing their rifles at each other at a comparable speed. It just doesn't.
And just to sidetrack on terms of balance, OP is absolutely right that the M1 Carbine has the DPS curve of a bolt action. It's almost identical to the DAK's K98.