[The Bard Rocks]

I prefer someone who does both, but am not stuck on that.

Think. If you sing, two things happen. First is music, a voice being a type of instrument. But secondly are words and meanings. No other "instrument" can do that and it is hard for a skilled instrumentalist to compete without singing at least some of the time.

Also if you are a singer, there are instrumental breaks whereby skill on an instrument can be demonstrated. An instrumental piece does not get vocal "breaks".

Last, little kids sing. Singing is something nearly everyone has done, in school, in church, singing along with the radio, wherever. Most singers just do it and don't take lessons or learn how, not like it is for anyone learning an instrument. (I don't mean to imply that singers can't learn later in life or take lessons, many of us have done this as well.)