Yes, perc + shotgun come very close. Yes, I realize that. I've used it. Many players can't consistently use it. (See the end of my reply.)
Yes, but if I have the HVR at a long range, my opponent isn't going to pop their head out. The thing is.. OPGL, PMG, and Shotgun aren't cheese-mode if you're forced to fight in their range.
I guess what I'm saying is, somebody who is a pro with percs + PIG will stomp on anybody forced to fight in their range, which missions will do occasionally. Somebody with perc + shotgun might be able to stand up to them if their pellets land correctly. Of course, this doesn't happen consistently. Hell no. It's hard to do. But in the hands of someone who rarely misses with their PIG and consistently achieves the near-instant TTS it feels ridiculous. I've experienced it a few times. My stance is that it would be nice not to nerf the PIG or Percs so that all the other players can't use it, but the near-instant stun should not exist to be abused by someone who can abuse it. Maybe it's not possible to achieve that, but that's what I think.