> Or maybe test coverage has/will become too noisy a parameter to use at all.

It already is, ive banned unit tests via ci checks from our codebases, they were not particularly useful before LLMs and now they are a net negative.

We require int and some e2es and that does all that units do and more.

Are they slow and brittle?

I like having both. Unit tests are a decent indicator for local development. Fast, quick to iterate on. Integration tests are slow as molasses and I can’t iterate with them when it takes 20 minutes to setup the suite and run everything. Too slow. But still useful as you say.