Fear of missing out is when there is something going on that will soon not be there anymore, and you feel extremely compelled to take part.
Atelophobia is defined as the fear of imperfection/not doing everything you can in a situation/not being good enough, which feels closer to what you are looking for.
If you are taking part in ALL forms of content with multiple alts, that sounds like obsession, since a lot of the things you mention will still be here in the years to come. I suggest not doing literally everything WoW throws at you, because you won't have time to do anything else. Why do you need exactly that trinket? Why do you need another recolor from yet another 1% chance rare mob? I agree it is a stupid system, and I felt like you some time ago, but I decided that my mental sanity is worth more, and whenever Blizzard throws low-chance stuff at me, I just pretend it isn't there.