Are sprints bullshit? Maybe some of them. But for teams to be effective, you need communication, knowledge sharing and some form of tracking progress. A good manager facilitates these items. A bad manager just throws tickets on a Kanban board. Sure, if you have a team that can do all the above without sprints, that's great. But I bet they have some other method or social structure that makes team management effective…
The real problem, of course, is the word "sprint", which (whether you like it or not) implies something.
A sprint, be definition, is unsustainable.
It's Pythonic levels of hilarity that we adopted this word to describe software development. It's Shakepearean in the tragedy that so many defend it.
Choose another word, like, "jog", "amble" or similar, and you won't see the same level of backlash against it.