I agree, claude is an impressive agent but it seems like it's impatient and trying to make its own thing, tries to make its own tests when I already have them, etc. Maybe better for a new project.

GPT 5 (at least with cline) reads whatever you give it, then laser targets the required changes.

With High, as long as I actually provided enough relevant context it usually one shots the solution and sometimes even finds things I left out.

The only downside for me is it's extremely slow, but I still use it on anything nuanced.