What even is prestigious about anything in WoW anymore? Maybe it's just me but that feeling of awe when inspecting people in their BWL/AQ40/Naxx gear has been lost probably since Wrath, and even though the mythic raids we have these days are mechanically far more complicated and difficult than any fights back then were, seeing someone in their full mythic t19 or 20 just makes me think "Oh, god.. You still have the time and drive to raid?"
Not even PvP is really prestigious anymore, I was still impressed in Mists and Warlords when I would see someone with Elite Gladiator gear, but now there is no PvP gear and the only notable rewards are received after a season is long over.
The only things to me that still hold prestige are the difficult to obtain, time limited titles, mounts etc. Things like Vanilla PvP titles (YES I check achievement dates on people with RBG titles), Scarab Lord is probably still the most impressive thing in the game, I'm also still always impressed whenever I see Benediction/Anathema, or Rhok'delar. The BC titles, Hand of A'dal and the other Naaru one, Black and Plagued Proto-Drakes from Naxx achievements, Green Warlock Fire from Mists, surviving WoD and now challenge appearances in Legion. As well as any Gladiator title, or any title given to the first group to kill whatever boss on whatever difficulty (my favourite being "Death's Demise" from Yogg+0)
These days WoW needs accessibility to survive and Blizz have done superbly well to keep it alive. Gamers have changed, no one coming into WoW in 2017 is still going to be playing in 2 years time if they see someone in the best gear and just think "Oh, I don't have 40 hours a week to play this game I can literally never reach that level."