I have no idea what "an active harness" is referring to, Appium looks like a cross platform testing framework.

I doubt it brings any advantage over XCUITest here.

What is supposed to be the problem with parallel development? I use worktrees, and it works just fine with five agents in parallel.

Automated end-to-end testing on mobile is notoriously flaky, but that's nothing new, and I think it is now much easier to deal with.