Absolutely, when stuff runs fast it's better UX compared to when the stuff runs slow.

I think what parent comments suggest is, the speed of applying a diff is not the major bottleneck in LLM-assisted coding, and improvements in other aspects are much more desirable (e.g. correctness, or even speed of thinking models themselves).

In a world where diff application is a real pain point, it's likely one of the last pain points in the field.