> But if you actually have made things complicated enough [...]

The only problem I see in this case is that complexity doesn't come all at once. By the time you reach a problem that k8s is good at solving, you've probably already accidentally made a k8s alongside your piece of software.

In my(quite short) SWE career, I've seen software evolve, even ones with a proper design stage. Maybe I just don't have enough experience to have seen a properly designed project, but I don't know what I don't know after all.