He's spot on about separating "configuration generation" from convergence. There is no reason for the two to be the same system, the same tool. As he says, Kubernetes is only concerned with the latter, whereas Puppet, Chef, and Terraform conflate the two (insofar as it uses HCL).

And for all the talk of "declarative", there is no reason why the configuration generation stage cannot be imperative, a la Pulumi. It is the desired end state - the catalog that's being generated - that is declarative.