I can't say for sure unless I was there, but if you were using those guns on Platinum and you were doing well, it was most likely your other teammates doing most of the work or you were consistently getting headshots or you were relying on your powers because those guns are straight up trash (relatively speaking)
also I'm specifically talking about people going into lobbies with Avenger 2s and Shuriken 5s and Phaeston 3s and stuff. really, you should only be using these guns if you plan to only use them to apply ammo effects on to foes so you can detonate them and you don't happen to have a better alternative (Avenger/Phaeston for the lack of Hurricane/Collector SMG/Lancer, for example)
honestly, a Claymore or Reegar Carbine I is better than a Katana X. a Hurricane I is either leagues better or matches the effectiveness of most non-Ultra Rare assault rifles at X, as well.