Sidearms are amazing...
I haver 5,712 kills on my Lonesome and 3,082 kills on my Keening. (all crucible kills). And my Keening isn't a fantastic roll. I've probably sharded a few hundred god rolls. My Keening has Threat Detector and Vorpal. I find it fun to kill a super with a sidearm. My Lonesome isn't a fantastic roll either, but they both work for me. I've won a 1 v 4 in survival with it.
I'm not great in the Crucible. There are young whipersnappers that can out play me. If it comes down to up close and personal, I'm in trouble. That is my weakness. which is why the sidearm comes in handy. I back up as the sliding shotgun apes come at me and they are puzzled as to how I took them out.
Sidearms can really mess up a shotgun Ape...because they all either use a / their Traveler's Chose quest-reward "Mindbender's Ambition", "Felwinter's Lie" or "Riiswalker". If you are remotely good at aiming while backpedaling, they die, especially with a Suros (Full-Auto Machine Pistol) sidearm or the Omolon (3 Shot Burst) sidearms, especially if they Tap the Trigger or Zen Moment as perks. Simply because with the Suros ones you can backpedal and center-mass drop them in no time and it's very easy to get 2/3 shots from the Omolon's burst into the dome (if one could roll with Accurized/ AP Rounds, Zen Moment AND Headseeker....oh boy) and either make them back off or drop them about the time they get into killing range.
I like ones like Lonesome, Buzzard (again Bungie...WHY did you sunset ALL the Shadowkeep / Dawn (Saint-14 era) weapons?), etc. for PvE as a good backup for a FR or shotgun when I feel like doing a beat-your-face-in Titan build with Wormgod's Caress/Synthoceps/Feedback Fences, which usually means an exotic sword or Tractor Cannon as my exotic if I'm not using Duality...until they give me Invective back.
Each weapon has an area is should be in...and honestly, aside from sidearms, which aside from Trespasser I think were only single shot in D1...D1 had them all right at the end during Age of Triumph....why they didn't just wholesale-copy those standards for everything for importing into D2 I will never understand. Sure, there would be outliers, like High Impact FRs, and the new types of weapons like SMGs and Linear Fusion Rifles to consider, but it's not like that would have been very hard to keep all the others the same until you figured out where those weapons came into the picture.