Yup, it's time for a huge Valiant revamp 2.0. When people start using other units than Valiants, and not because of strategy but simply because there is better, there is a problem.
Kiera's revamp was good... I guess. At least for the now great Elem, and good enough RM.
But I'm really not sure about the MW and the Warlock.
MW is good. She's just outclassed by MW Zoey and her niche is quite specific. The opportunity cost for promoting to MW is not being able to get an Ele/RM Kiera. Ele Kiera had so many significant buffs it propelled her on par with Ele Zoey. While Ele Zoey would be better as teams thin out since her skill would then potentially hit just 1/2 enemies, Kiera offers similar amount of damage plus the possibility of a mass stun, which is insane. On the other hand, Kiera RM is the bulkiest mystic yet and trades the pure destructive power of her Ele counterpart for defense and non-position reliant global nuke that pops resilience and decimates clumped formations(oneshots everybody except MAG invested healers, mystics and defensive guardians, assuming enemies are clumped together) and I personally think she fares better versus guardian swap teams for the two tile knockback which is gold versus them. You have to forgo all that when choosing MW Kiera and she would only function similar to Talilock, popping double resilience heroes while being a good source of damage versus ranger teams.
Overall, I see no reason to use MW when Ele and RM are too good to pass up.