same here I only play one class. Never had it it in me to level an alt. Even on games like ff14, where you can have multiple professions on one char, I only play one profession.
I just don't have the time for playing any other class 😅
On my primary account I actually completed the core story on all 9 characters/professions. But from there on (Expansions + Living World) I did the story and mastery unlocks almost entirely on my 2 Mains. Sometimes following up with another character, if I was missing an important achievement, e. g. for a legendary trinket.
Well, I did the EoD story until reaching Kaineng (incl. Seitung map completion) for the Jade Bot stuff (and some missing hero points to fully unlock all elite specializations) on all 9 characters/professions on both accounts.
Map completion is a different story. I'm aiming for 100% (at leaast all hero points and all waypoints) on all maps and all characters (on 2 accounts). Which means that I'm not running out of stuff to do any time soon.
I liked completing maps in order to prepare my way to get legendary weapons with the gift of exploration. After I got all 1st generation leggies, I stopped and now I almost puke only thinking about doing it another time.
And for personal story, I only completed it once with a Sylvary and I loved it. Other characters, only done until our beloved friend dies.