Depends on what kind of m+ you are talking about.
Do you mean starting from zero with aim getting KSM?
Do you mean already have 1 character at KSM level and playing it as an alt?
Do you mean from a pov of a player running multiple alts at 15s for weekly vault wanting to add one more?
Do you mean pushing around 20s? Do you mean trying to get world first as mistweaver?
Well at this point of the game and with most people running around in 217+ you can pretty much time any dungeon up to 15-16 with any random combination of classes assuming people involved in the run have experience. Itās all about the players and not the class at this point. Thatās the reason you see people failing with 5x 220~ gear while other can run 4 + 1 fresh 180 alt.
Yes mistweaver is not resto shaman that you can heal more easily but then again its kinda harder to push enough dps as resto shaman if you just spam the party non stop (before the ele lego ofc).
What is more crucial in a m+ is to get familiar with the popular route almost everyone uses on every dungeon, break down in your mind how the average party performs and distribute your cooldowns accordingly. Im not really in the mood of running very high keys but i can for sure at 220 heal 15/16+2 without drinking just by using cds effectively. Also i like it now even more since i was using AoTM only up to 14 and now im using it to all my keys up to 17 (was ToM before) due to people being more geared.
Mistweaver pretty much cant compensate for bad groups. You donāt want to be in their group anyway, if you donāt mind being level a shaman heh.