I find that mock-heavy tests I've interacted with are low ROI: they don't find or predict bugs, require significant work to write, and often have to be updated

I find that mock-heavy tests I've interacted with are low ROI: they don't find or predict bugs, require significant work to write, and often have to be updated when the code under test has changed even when the actual feature/case being tested has not changed. While mocks can be useful, IMO "never use mocks" isn't a terrible rule of thumb.