I say you'd have to restrict it to primary, secondary, exotic. My list will be all inclusive, pvp and pve both equally in mind
Primary Red Death: Health regeneration after a kill especially in those days of no chalice crota strikes. It's always been a beast in the crucible as well
Secondary Patience and Time: The absence of a Y2 Ice Breaker is mainly the cause of my decision here. I've always preferred snipers on the countless FPS games I've played Hereafter is a shell of an exotic, spindle while great PvE has no real use in the crucible as its exotic perk is situational and requires a large amount of skill to make useful, the same can be said for Zen Meteor, now cloaking is useful in both scenarios even though it's restricted and not exactly 100% invisible but it shouldn't be in my opinion.
Heavy Thunderlord: Pre Field Scout nerf this gun was able to outgun any LMG in the crucible and still a favorite of arc burn nighftalls the hidden Firefly perk added a nice theatrical spin and came in handy while clearing adds.
Can I put none of the above? Seen as TLW and MIDA are getting old after 2 years of overuse. And Spindle is an exotic version of an amazing sniper. And Truth is a nooby weapon in Crucible. And Tlaloc is warlock exclusive making it less useful.
I'd say the Fabian Strategy. It's one of the few year two primaries that actually feels exotic. First off, it has great perks. Life support and Crowd control? Yes please. Second, it does something that no other gun in the game can do: change its fire rate based on enemy proximity. It is an 88/8 auto, but it transforms into a 100/2 when you need to get up close and personal. It's the gun you need, when you need it.