First let me state that WW, the spec you are most likely to play in open world, is incredibly strong at doing quest, rares etc. In Warmode you become even more powerful in both offence (Turbofist) and defence (Turbofist/Reverse Harm). The only rares you should have trouble with are the 4mil+ ones in Naz/Mecha (which a lot of classes cant solo). You also have a lot of escape potential from ganks and bad situations in general.
If you don’t play with Warmode then it is true you will be weaker, but the addition of Reverse Harm as an Essence will really fix those weaknesses.
Brewmaster
Raiding - You’ll be a strong tank for 99% of guilds. Almost no guild ever thinks “Oh how terrible a Brewmaster”. In addition you are arguably the best tank for prog when players are undergeared. One complaint a lot of BrM have is that they are not very self-reliant. You aren’t a Blood DK, you take a long time to die, but without a healer you will die.
PvP - You’re an alright flag runner, thats about it.
M+ - Dead middle of the pack, equal with Palys, stronger than Bear/DH (although the tank buffs that just came in may mean this is no longer true). On weeks that favor mobility you will feel especially strong. Should have no problems pushing up to mythic 15’s, although you wont be the “ideal” choice.
WindWalker
Raiding - You are solidly in the bottom half of DPS. If you plan to push Mythic early in the tier then most hardcore prog guilds wont have space for you. There are some silver linings, WW has a lot of mobility, which can make many fights much easier compared to other dps classes. The self heals and decent defensives mean you are usually one of the last to die.
PvP - Currently very strong in arena, if you plan to push to 2.2k then WW is definitely an option, bonus, other melee classes will despise you. In Pug Battlegrounds your ability to pick your fights and disengage makes you very fun, but you really will struggle in Premades.
M+ - Without a doubt you are one of the Strongest M+ classes in the game. There is nothing much else to say. There will be room for you all the way up to Mythic level 20 keys, and I presume even higher.
Mistweaver
Raiding - Solidly middle of the pack. While it is true your healer cd Revival is lackluster, your general throughput healing is incredible. Heavy tank dmg? Heavy ticking single target dot? MW is the healer to call. Your biggest weakness’s are mana efficiency, and your ability to blanket heal the raid. Once half+ your raid starts taking heavy damage, all you can do is hit the lowest health people and trust the other healers can cover this weakness. Mistweavers have at no point been a bad healer.
PvP - Strong all the way up to 2.2k, still strong after that although with less comps. Very popular healer. You do have some weaknesses that force you to preempt damage/burst windows, but if you plan to go hard in arena then you need those skills no matter which healer you play. In battlegrounds you are the best healer. Most premades will want to run 2xMW because of the high amount of throughput.
M+ - You can do everything comfortably up to 15s, and while you could definitely push higher, it might be hard to find groups due to the Resto druid dominance.
PS: Limit used 1xWW 1xBrM 1xMW in their World 2nd Jaina kill.
PPS: Pieces used 2xBrM in their World 1st U’nat