I am mainly parroting things other people have said in other forum posts and facts we’ve known since beta. Just condensed by me into an easily digestible format.
Brewmaster is the worst tank right now, by a huge margin. In beta raid testing, brewmasters required on average 500% more healing to keep up compared to prot warriors. Which would be understandable in the case of, say, blood dk that heals all that extra damage taken back. But brewmasters have no such advantage. Not much has changed in the relative power levels of these classes since then.
The recent nerfs have only widened the gap, as brewmaster is getting into one-shot territory from tank busters. Big offender being Guardian Sentry in Algeth’ar Academy. He casts Storm Slash every ~10 seconds on the tank, which is enough to one-shot a relevantly geared brewmaster at around +20. A popular tank streamer Dorki, was doing +18 Algeth’ar on PTR and 1 melee + 1 storm slash was enough to kill him. Even blood dk’s don’t die to that on +18. So much for smooth damage intake.
Speaking of smooth damage intake… a common argument people often have about brewmasters is the smoothness of the damage intake. However… Prot warrior on average takes LESS damage on the initial hit than a monk does when staggering 70%. Think about that for a second. If stagger damage just went away, monk would still be a worse tank. That’s how far off balance is right now. It isn’t “smoothed” damage, it’s just more damage. A LOT more.