Vex..... 😂 😂 But joking aside fusions do get used a lot in pvp even if they aren't in the leader board for weapons in trials.

you're probably in a higher skill bracket.

Actually I think I found one answer. In comp, the null composure is at an amazing .69%... Edit: Apparently people have been using the null composure in PVE.

Yes, as other people told you legendary fusions are everywhere. Mostly in PVE. For example: https://destinytracker.com/destiny-2/db/insights https://guardian.gg/2/weapon-stats/3/4/0/2021-08-17/2021-09-17 In PVP, the shotgun & slide nerfs have not been able to push shotguns away from the top specials spots, but the use of fusions is slowly coming up.