I only offer this to illustrate, not because I think any of this is relevant to a potential ME PvP.
When I played CoD: WaW multiplayer on the 360, the game had been out for years. The hackers (always wondered why people think you can't hack Xbox) were rampant, probably in 50% of games. The competitive players had long since sorted out all the spawn camping techniques, and nothing was quite as annoying as their ability to throw a grenade with perfectly cooked off timing.
If I just ran into a random game using smgs/shotguns/rifles and attempted to play a standard run and gun style, I got my ass handed to me. I couldn't aim as fast as them, I didn't know the tricks, and even after I reached my peak ability knowing the maps etc., I still wouldn't see an even Kill/Death ratio at the end of one of those games, though sometimes I could get close.
I've forgotten the name of it (Mosin Nagent, I think) but the game had an old Russian single-shot sniper rifle that you could unlock around level 20. Once I got my hands on it, it became my weapon of choice. It wasn't because I have good aim, and it wasn't because I could quickscope (still can't.) In fact, across almost every shooter I play that tracks such things, my accuracy is about 60%. That's objectively terrible, especially by PvP standards.
But I do have a couple of things going for me that most CoD kiddies don't: I'm smart and I have patience.
So eventually, on just about every map, I figured out my sniping positions. I would rotate between them as soon as someone got it into their head to find me. Yes, a good player trying to track me down would eventually get me, and then he'd have to figure out which of my sniping points I switched to. If he was smart, he would eventually move off from me, because the effort to take me down wasn't worth the results. If he/she wasn't, they would keep trying to get revenge on me and pay for it with many deaths.
They had "bouncing bettys" and these were essentially my "spotters." I always carried them. There was one perk in the game that let you see them, and anyone determined enough to take that perk was going to get me easily, but anyone else was going to send the message "bouncing betty killed <blank>" and then I knew it was time to move.
Using a Mosin Nagent (I'm now quite sure that was the one) even with my terrible aim produced an average kill to death ratio of 12 to 1 for me, against competitive CoD players who were way better at the game than I was. It was basically the only way I could even compete. The only deal was I had to be patient. I had to take good shots and avoid giving my position away on marginal ones. Sure, most of the guys topping the scoreboard had more than 30 kills, but even the really good ones had 10 or 15 deaths to go along with it.
Me? I preferred my 12 to 1 ratio. I don't like dying in video games, and I'll take it slow and cautious if I have to.
I don't think anyone in the CoD universe was calling the Mosin Nagent an OP weapon. There was a multi-shot semi-auto SR unlocked at level 50 that was ridiculously OP in PvP terms. But, in practical terms, this was rarely an issue, because only a tiny minority of players ever used either of the two rifles.
Most PvP players do not have the skill to use a single shot SR effectively, and will never touch it. Even rarer is someone like me who lacks the skill but uses it anyway because he has the patience to wait until the right moment to strike.
Single shot SRs do offer a huge advantage, but the vast majority of players won't use them, regardless. So they don't really end up dominating the game, with the exception of a small minority of hardcore players who would dominate regardless of what weapon they were using. So, really, the only people making the SS SR overpowered in PvP terms are, well, the rare birds like me.