"they'll be able to pick up your language no problem."
That still takes time. If someone is already experienced in an (complex) ecosystem, he or she will be way more effective in it, than someone who has just general skills. I guess I am a very good problem solver. But if I suddenly would have to do a C++ project with all its footguns, I am not aware of (last time I coded in C++ was in university)? I would suck in it for quite a while. This would not be effective at all, unless I would want to change my skillset to the C++ ecosystem.
That still takes time. If someone is already experienced in an (complex) ecosystem, he or she will be way more effective in it, than someone who has just general skills. I guess I am a very good problem solver. But if I suddenly would have to do a C++ project with all its footguns, I am not aware of (last time I coded in C++ was in university)? I would suck in it for quite a while. This would not be effective at all, unless I would want to change my skillset to the C++ ecosystem.