Like I said WHM relies more heavily on its partner than just about any other pair of classes. WHM is good at pure healing which is basically never needed and bad at mitigation which is always needed. Having to heavily rely on the shield healer doesn’t make it viable, it just increases the stress on the shield healer. WHM simply doesn’t have enough mitigation to compensate for the fact that healers in this game are basically glorified mitigators.
AST gets 3 mitigations per 2 minutes plus an ability to spam shields, WHM gets 2 and they both HAVE to near overlap for some ungodly reason, it’s mitigation capabilities are weaker than some DPS classes and more rigid than any other class in the game (every other class has at least one mitigation on a shorter CD than WHM)
AST and the shield healers simply do not struggle with throughput enough to warrant WHM having so little in the way of useful mitigation in the 1 in 10,000 chance that WHM’s higher HPS might save a run over AST who near equals it in HPS. Thats why I drew the comparison to double regens, because they show that WHM has a deficit. Double shields were meta basically all of EW and only aren’t now because AST is so ridiculous on the damage front. Double regens on the other hand are a meme comp, and AST has basically twice the functional mitigation of WHM. Anecdotal I know but I don’t know a single shield healer main who actively wants a WHM over an AST, hell half of them want the other shield healer over WHM
It’s just very hard to see if you haven’t seen it from the shield healers side that WHM is very good at making you think you are contributing while in reality you are just making the shield healers job harder, doing 80% of the “work” AST does forcing the shield healers to do 120% to keep up
And this isn’t even actually WHM’s fault, it has strengths but square refuses to design encounters to play to them. I’d rather square ups damage to make WHM’s contribution more useful over making it a pseudo shield healer like AST, but until they do that WHM just doesn’t bring anything to the table