WHM was better in dungeons in hw too if we're going to use healer's dps as the discriminating factor. A good sch can still easily reach 2k dps in a dungeon and its single target heals are very solid, probably stronger than whm's. But that's not the point the op's trying to make. He's suggesting that sch's healing capabilities are lackluster when compared to ast's and whm's. This is absurd. SCH was and still is the best single target healer, if he's struggling keeping the tank alive during big pulls, it just proves that he's a very bad sch and he's not using his toolkit correctly. Of course, st healing is way easier on whm/ast, you just stand there and spam cure2/benefic2, or at least this is what most mediocre healers tend to do but it works for trivial content.
Miasma 2 can and should be spammed if you have spare mp.