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

[Rilifane]

when is the balance not on fire.

Rarely.
Healer channels are very civilised. People ask questions, people get answers. On some rare occasions a feelycrafter pops up and gives bad advice, gets corrected by more knowledgable people and that's that. I don't read other channels too often but they're pretty much the same.
Only time Balance is on fire is when they make changes to pander to people that don't care about something while angering people that do, e.g. ShB healer change overall, initial removal of ED, SD change etc.
So no, Balance is not constantly on fire. When it is, it has a very good reason to be.