Why is the healer class basically a one spell dps class?

[Absurdity]

Partly. The other major issue with the cards is some of them were effectively useless.

EWER redraw EWER redraw BOLE

Not really useless, just incredibly niche. Like I said, I'd take an enhanced bole over a balance any day when I got a tank that wouldn't use mitigation if you replaced every other skill with it.
In savage you don't get those people and even in dungeons they're not all that common, so unfortunately you didn't get a lot of use out of those niche cards.