Remember--I was very young when CSI started.
I thought the oldest guy was listed first in the credits--not that he was the star! Paul/Brass was listed last because he was more of a co-star, but all the original team--Grissom, Catherine, Nick, Warrick, and Sara--were equal stars so that was why it was called an "ensemble". (I'd guess I got that from hearing "ensembles" sing in church!)