There are other than 1 shot sniper rifles? I didn't notice.
I think you and I are gonna go along very, very well
You on PC? We could BOOOM some melons together.
I'm going to put two words in a sentence that should never belong together. Without reload canceling, the Claymore would suck.
Does not compute. Would taking away reload canceling change its sound, somehow? 
I am a fan of RC, but I do have to admit I was frustrated when Claymore GI were OSOK everything while BioWare was nerfing the hell out of Sniper Rifle TC, and doing nothing about the shotties. I got over that when they finally rebuffed every SR, but the Valiant.
This has nothing to do with Claymore (or other powerful single shot guns) and everything to do with the inherently broken infiltrators, GI being the most broken of them all.
The problem of sniper rifles wasn't so much the damage but the shield gate, which pellet-based guns could always work around, while single-shot weapons never could, until the introduction of Phasic Rounds.
I happen to disagree, somewhat. Infiltrators, with the GI on top, being broken is out of discussion of course.
But it's not only that. Shotguns are, objectively speaking I think, badly balanced for this game, in and for themselves.
And the reason is one, and one only: smart choke. Most overpowered piece of motherfuckingly awesome mod ever conceived 