I read this a little differently. Personally, I think all of these weapons are actually great, it's just that the completely broken weapons are so far above that it's not even a fair comparison.
The MP7 rips close range. It has a good ammo count for the damage, and you can wipe a whole squad with good shot placement. The AS205 is a mid/long range beast, and consistently gets me kills on players who think they can challenge me at range. Same with the 556, but the 556 also has better punch at close. QBZ rocks a good ammo count, and like the MP7 can squad wipe with good shot placement, AND has pretty good range. UMG is a longer range weapon, and again, awesome ammo count. SOR ACTUALLY kind of mid, but I still found it to be a reliable weapon with repeatable shot placement. LMR is NOT a killing gun, it is a harassment gun. I've used it with success at poking enemies out of cover for my team to catch off guard. SL9 is a beast, and everyone sleeps on that gun. RPKM is a good mid range contender, and has reliable shot placement AND good ergo.
Again, there isn't anything BAD about these weapons, it's that the broken weapons are overtuned and make the bottom look terrible by comparison.
I'm level 20 on almost every weapon, minus the M277 and about half the pistols. Mind, most of that was PRIOR to the XP changes. I have a pretty good idea on the performance of each, and how they stack against each other. In reality, most of the weapons are just a carbon copy with a little bit different fire rate and different model. Player skill is still the largest determining factor to weapon performance, and with high level players, they will naturally only focus on hyper-meta builds and that blinds them to the larger picture on weapon balance.
There is no point listening to a high level player who has 400 hours on one weapon, and only touched another weapon for a few matches before deciding it didn't outperform their meta gun, and they move on. If your standard is UI Goku, then SS Goku will always seem like trash.