It's a judgement call to say kube is at its heart workload scheduling, and I don't think it's true.
For a while some of the managers were packaged together into some core, but that's no longer true. Yes it still resembles most people's use case too. But neither of these technical truths convince me that this incidental happenstance is a core truth.
I haven't heard any arguments for why you think it's "too complicated" to be an extensible platform, and I struggle to imagine what you would rest those arguments upon. There's a restful API server and folks watch the api-server with operators and write code to make sure the real world resembles that desired state, best as they can. There's so many hundreds of operators, and it seems not-hard for many. So, like, what's so scary about that?
But you insist on calling it "a dumb scheduler API" which again is using bad definitions to argue a bad point that you can't make in good faith recognition of what's actually at stake here, that contorts the view to a dumber simpler wrong view of what's happening.
> Seeing Kubernetes broken up into smaller, more purpose built components and let folks pick and choose or swap could be helpful
This is the exact opposite of what most people ask for, which are integrated kube distros. And they ask for that because kube is a collection of different isolated pieces that happen to compound into something bigger. You already have your wish, you just don't see it.