I think the argument is that pyromancer has lost a bit of her identity, not that pyromancer is weaker.
Edit: It used to be 15% in the beta, which meant it was always the best choice. You have to keep in mind it’s an increase to overall damage (and not merely the stagger damage bonus as the other talents are) it’s much more competitive with them than it looks. It also affects ranged.
To demonstrate, here’s a link to the quick testing @BizarreSalp did. There might be newer numbers somewhere, I can’t recall where.