There are things that are painful to express in a pure functional language. I'll give you an example: rasterize a triangle to a mutable buffer. (An inherently mutable and stateful algorithm). You can certainly do this in a purely functional language, but I doubt it will be any clearer or more performant than its procedural C counterpart.

I think pure functional programming is super useful in other contexts, for instance, a compiler. I'm weary of people suggesting that a specific school of thought is universally applicable, though.