I installed and mantain a private Cryptpad. I'd say scripts loading from two different domains (usually it is the same machine and webserver) is an important part of the privacy model they have.
Loading pages of a Cryptpad setup is not as fast as, let's say, Etherpad, but the use cases are quite different, and we are talking about 5-10 seconds to login. I'd say cryptpad.fr is a nightmare to mantain compared with the one I do.