Agree with your bit about the vocalist, sort of.
With our current band the vocalist chooses the majority of our songs, he knows if he can sing them in the original keys.
If any of the rest of us in the band want to do a song, we send it to him first, he will initially try it out, if he is certain he can perform it in the original key, it gets his approval and the rest of the band can start learning it.
We have yet to choose a song that is out of his range, if he cannot do it in the original key he has no interest in doing it anyway.