Frankly, he's more of a critic than a writer.

Literal

Frankly speaking, he [topic-は] writer [rather-than-というよりはむしろ] critic is.

~というよりはむしろ ('rather than X, more like Y') refines a characterization, replacing one label with a more accurate one. Here the speaker reframes him from 作家 (writer) to 批評家 (critic) — a barbed assessment that he produces commentary on others' work rather than original work of his own.