Earlier quoted context omitted.
I agree, but with a caveat - there's an important time/value tradeoff to going down any particular rabbit hole where you have more tasks than time to expend on them, particularly if you're in a billable or result-oriented area, and it lacks obvious benefit. There are plenty of times I've seen people think of things as "well, it just does X" because of a lack of depth of knowledge, but you also can't necessarily go do…
I disagree because things like flappy tests are a "smell" that could lead to discovering a deeper problem. We simply don't know ahead of time that the payoff won't be worth the effort in such a situation. If you can't explain what's wrong, that's bad.
Not ever having engineering time to investigate why it's unreliable is a (mostly) unrelated problem.