Well, the thing is that based on my experience with Swift and Xcode, I think maybe it hasn't. (Has it?)
And at least part of the regression in build time hasn't been fixed by Xcode 10.2.1, see here.
Instead of thinking “sure, of course there are tests for that, at least now”, I’m just feeling more and more like a full time Swift/Xcode forever-beta tester and bug/workaround-detective, and less and less like a productive app developer, and it saddens me that it hasn’t gotten noticeably better after all these years, which I really thought it would.
It’s still common to see seemingly basic and very noticeable non-niche stuff be more or less broken in a GM, and we have to deal with them for months on end.