Priest is literally the worst class this patch (and struggled through the whole expansion); Shadow was doing fine but got nerfed to the ground, it’s healing specs are viable in raids (but so are any of the other healers) but garbage in M+.
Boomkins and Eles deal a lot of rot damage in bgs, but they lack the power to secure kills that most mdps have either through raw power (i.e. Unholy) or by locking down an enemy through instant cc (i.e. Fury, Havoc).
Don’t even start with off-specs, all of the tanks are well balanced.