It's criminally bad. You can't copy logged variables. You can't inspect worker threads (!?). WASM support is practically non-existant. You can't even do a heap snapshot on demand, something that should be a basic feature.

The timelines view is practically obfuscated with pretty graphs that show some aggregated data and some automatically generated snapshot points where the dev tools decide that are meaningful.

Inspecting the rendering pipeline is impossible. You can't see memory usage, compositing reasons, long frames (you kinda can but it's tricky)...

Not even going into remote debugging for iOS which crashes either the dev tools or Safari on iOS in any non-trivial scenario — the exact ones you need a debugger for.