I haven't heard of much activity in the 90-99 bracket.
Someone correct me if I'm wrong here but I believe that 91 was a 'thing' because of certain scaling factors/gear availability.
I'm pretty sure people levelled up to 99 after legion or WoD as the niche that was keeping them at 91 subsided.
At the moment, due to level queue separation you won't find a battleground with locked xp and I haven't heard of any organised wargames happening.
I have a level 90 collecting dust, was debating going 91. Is there any point?
I think a big part of 99s was the fact that you could get your artifact weapon - However with their effects being disabled, i doubt they're much better
Pretty sure they've been dead since armor nerf or whatever
Outside a BG you might find that level 91 can get better secondaries