CRDTs are not inherently “crazy slow”. Researchers just don’t succumb to the appeal of premature optimization.

See: https://josephg.com/blog/crdts-go-brrr/

(And even these optimizations are nascent. It can still get so much better.)

The section you quoted describes an effect of homomorphic encryption alone.

There is the problem that both CRDTs and encryption add some overhead, and the overhead is additive when use together. But I can’t tell if that is the point you are trying to make.