I'd recommend Beyond Light and Lightfall just for the subclasses alone. BL also has the added bonus of having decent story. I vehemently hate LF so the only thing I have to vouch for it is funny green powers.
You should keep at least one character I think. Sometimes you get different dialogue for having a 'veteran' character based on your achievements! idk how often they do it anymore but I always found that lol flair pretty neat
I'm a weird Hunter who ignores the meta in most cases. My favorite exotics are Liar's Handshake (Knife Hands), Gyrfalcons, Caliban's Hand and Orpheus Rig. I tend to just build around their gimmick without much thought. Hands down my favorite exotic weapon would be Witherhoard (affectionately nicknamed Coom Cannon). It's a great ad clear and decent fire and forget boss dps. Use it all the time in content I have to try in.
Uhm I'd also say at least start Witch Queen because that should unlock weapon crafting which should be pretty fun! Not every weapon is craftable but there's still a lot compared to launch.
All in all, I'd recommend at least going through the campaigns. There's a lot of content in those years that you've missed out on, and that should give you enough time to mull on the idea of sticking around or not :3