I would say that practicing in a long-compile-time environment is part of improving your skills, but that once you have a certain level of skill with a language

I would say that practicing in a long-compile-time environment is part of improving your skills, but that once you have a certain level of skill with a language and tech stack, then it is beneficial to go back to having compile times of a few seconds or less. Generally speaking, it is far better to have a rapid iteration time to quickly test that the ground you are working on is solid as you progress. But definitely having a phase where you are dealing with long build times helps you enhance one aspect of software development!