My 2 cents on the Mistweaver set bonuses:
2 piece: The bonus doesn’t really change a whole lot. The biggest impact is that it allows for more reliable double mastery proc thanks to essence font HoT effect allowing for the mastery to proc twice. It goes up to 4 seconds when Fistweaving.
Not only this bonus heavily favors Fitsweaving (which I prefer personally but I don’t find it fair) it also sounds really really bad for Upwelling builds (since you re-apply the HoT on top of each other outside of Raid so the increased duration of the HoT has little to no impact beyond the very last bolt).
The Mistweaver has way too many interactions related to Essence Font at the moment. Essence Font is an excellent spell in raid but is really horrible to use in any other content. Currently it’s being used in M+ only because you made Ancients Teachings of the Monastery triggered exclusively by the use of Essence Font. Putting even more emphasis on Essence Font will create an even bigger gap (which leads to balancing nightmares) between the Raid and M+ performances of the spec. I would strongly recommend to avoid any interaction with Essence Font for both 2 and 4 pieces of the set. It’s already too overloaded (mastery + ATotM legendary).
The 4 pieces I haven’t had the chance to try out yet but to me the design is problematic. Either the bonus is really impactful and Mistweavers are then stuck in a very rigid playstyle where moving is heavily punished (at least a third of the time) or the bonus is so minor that Mistweavers don’t care about the rune and benefit from it rarely (which basically means the set is useless if that were to be the case).
I don’t know many players that enjoy a playstyle where moving punishes you, especially for a melee spec. For a ranged spec I could get behind it to some extent. Quite a few specs are very immobile and get away with it. But again the issue is that the Mistweaver is a melee spec. Even if you are allergic to the Fistweaving playstyle you are expected to stay in melee most of the time simply because many interactions work in melee. Leg Sweep, Spinning Crane Kick (mostly for Mystic Touch application in this case), the Nightfae entire covenant and simply the entire DPS of the spec rely on melee range.
Melee specs are already heavily penalized by how the game is designed, adding another arbitrary layer of restriction that doesn’t bring anything fun to the table isn’t a good idea in my book. Not only that but to me the Monk as a whole is the definition of mobility in current WoW. It’s one of the two very mobile classes in the game so making a tier set that expects you to play against the whole identity of the class is really odd to me. It would be like having a set bonus for Mages that has a moving area they need to stay in to get damage, it wouldn’t make sense.
So what would I suggest since I’ve been fairly critical of the set as a whole ?
First of all Mistweavers are very far behind in terms of damage but are doing pretty good in terms of HP/s at the moment (and the double legendary should make HP/s even more reliable). As several have suggested I would say add a damage component to the set, and a substantial one if possible.
Secondly the healing component needs to be on anything but Essence Font specifically. Renewing Mist or the mastery are the best candidates in my opinion as they are the only parts that are as used for most Upwelling and Fistweaving builds.
Here are random ideas:
Crackling Thunder is now an instant debuff cast onto an enemy. Other actions can be performed while the effects of Crackling Thunder are passively channeled. For any Tiger Palm, Blackout Kick (including its extra hits) and Spinning Crane Kick hits done while Crackling Thunder is channeled a stack of Grumbling Thunder is generated. The next Rising Sun Kick consumes all Grumbling Thunder stacks to electroctute all targets nearby. The damage is split evenly between all targets. Maximum 10 stacks. Crackling Thunder has no duration but ends when the target dies or Rising Sun Kick is cast.
Soothing Mist is now an instant buff cast onto an ally. Other actions can be performed while the effects of Soothing Mist are passively channeled. For any tick of the Essence Font healing over time effect (including the Nightfae version) and Renewing Mist healing over time effect an Appeasing Mist stack is accumulated. The next cast of Vivify or Enveloping Breath is empowered by the Appeasing Mist stacks healing all targets affected by either Renewing Mist or Essence Font. The extra healing is split between all targets and cannot overheal.
A lot of other things less whacky could be considered like Renewing Mist boosts, general damage boost or targeted to specific abilities.
In short, please don’t tie bonuses to Essence Font, please don’t make the power force Mistweavers to stop moving, it’s a very mobile class, and please put some significant damage boost in the bonuses so that Mistweaver can be a little bit more competitive outside of Raid.