It wasn't really one thing with Kubernetes that was slow, but that the more we tried to optimize it the less of core Kubernetes we were using and so the less value we were getting for the complexity tax we were paying. The image pulling you mention is a good example of that; having pre-pulled images is a big factor, but we have too many images to push every image to every node, instead we'd like the scheduler to be aware of which node has which image. We could do that with node affinity, but what we'd end up building would be more work than if we wrote our own scheduler to support it from day one.
> From what it looks like in your repo it might be that you need to do session timing (like ms) response time from a browser?
Our goal is subsecond container starts. We're not there yet, and might not get there with Docker, but we have a POC that is there with WebAssembly-based workloads. Too bad those are rare :)
(By the way, I'm always happy to chat about this stuff, my email is in my profile)