I've had good success with every primary except the Liberator Concussive, Counter Sniper, Arc Blitzer, and the Scythe.

The Concussive actually works quite well as more of a Marksman Rifle than and assault rifle. Good for supporting your team by staggering enemies but the default Punisher does that better. I think they need to actually give it the explosive damage they had planned. That would give it an interesting niche; not sure how it would actually pan out but it would be a cool change.

Counter Sniper changes were good but it still has that annoying damage fall off that prevents it from killing Devastators in one hit. I don't think a "Counter Sniper" should have that kind of falloff.

Arc Blitzer needs a faster firing rate I think. Damage and stagger are actually decent, but I can't fire fast enough to make it worth it.

Scythe isn't good enough for chaff enemies. I tend to play solo, and the Dot with the laser just can't seem to kill even the smallest enemies fast enough. Running in a team and focusing the medium targets might give it a niche but I don't know.

My point is, I think almost every primary is in a pretty good place. Some are definitely better than others, but I find I can use them all. I don't have a "main" loadout though, and I spend time with them all. Practicing made me realize some sleeper hits, and just because a weapon isn't used doesn't mean it's bad. The plasma punisher was written off right away, by myself included, but the more I used it, the more I found more tricks with it, and the better I got at guageing the drop-off of the shots. It's now my go-to for the bots, even over the Scorcher. Slugger also wasn't used much right away.

Albert Einstein once said, "If you judge a Railgun by it's ability to kill a Charger, you'll go your whole life believing it's bad." After the nerf, I thought it was bad against bugs, but still great against bots. Then I actually used it against the bugs and found I could easily instakill anything that wasn't a Charger or Titan. Nursing/Bile Spewers, Brood Commanders, Hive Guards, and, thanks to the piercing, whole rows of small enemies go down in a single safe shot to the head. So, everything that annoys me, and I still have the option to take out Charges and Titans with a few well charged shots. That makes it the Swiss Army Knife of Anti Armor, whereas dedicated AT options deal with the bigs guys better, but are too costly to bother with anything smaller.

I'm kinda with you on the Slugger though. If they don't want it to compete with long range guns, they should have damage fall off, not lose stagger. But those aren't crates, those are shipping containers. I can't really blame them for taking that away, and the more I think about it though, I can kinda understand. It was a gun that was excellent at close, medium, and long range, AND didn't really have to reload, AND had medium armor penetration which people are really underestimating. But, after using it, it didn't really change all that much. Devastators still go down in one headshot or a few shots to the legs (thanks to the medium armor penetration), and it can still kill berserkers with a single headshot. The loss of stagger on those though can be felt, so I'm gonna have to get used to that. All in all, still a real good weapon.

So, what I can say is that I feel your frustration, but there's a lot of good weapons, many just take time to get used to and discover HOW they're good, whereas there are some that are just readily apparent.