Brewmaster is still in a good place despite nerfs. I don't play the spec however.
Mistweaver has been the worst healer all the way through Eternal Palace but things are looking up with buffs in 8.3. We won't be kicking Priests or Paladins off the healing throne though, nor Druids off the PvP healing throne. Hopefully Shadowlands returns the spec to form aka return spells, abilities and skills that made the spec unique. Over Legion and BFA Blizzard have done a terrible job making it another bogstandard healer. See for example they reverted Soothing Mist from the abomination that was the Legion iteration to the Pre-WoD design in BFA.
Windwalker has been on life support for a long time now and the main theorycrafter for the spec has released an article on the Monk guide website saying he's dropped it in favour of playing Havoc DH, which is basically the same as WW but stronger, more mobile, and much more rewarding, forgiving and simpler to play. I don't blame him and I personally miss the WW gameplay from Legion. The artifact ability was fun to use and our mobility was in a good place.
Have a read if you want: https://www.peakofserenity.com/2019/...storical-data/