I think we got stuck on the term “musician”, I don’t consider singers as musicians.
I beg to differ. I consider voice to be the original God given instrument to humanity. Everyone has one, and it's my favorite of all.
That said, just like any instrument, it needs to be well played to be pleasing to the ear.
Singers are musicians. Their instrument is their voice. If you are getting a music degree with voice being your primary “instrument” you are taking the same classes and have the same types of performance requirements as someone playing the guitar or the cello.