Slice hit it on the head. I know Mesa just has you do a T/O and Landing from the right seat in the sim and this qualifies them for the right seat. As far as the guy being senior to the other, a CA's seniority doesn't matter if it is the other guys line. If both are RSV then the seniority wins the left seat. Although at least they are getting double time for the JA. This means that guy in the right seat was making at least $68 x 2= $136 an hour because he would have to be at least 4 or 5 year to be senior to that other 900 CA.
So as one can see it costs a lot of money to run an airline poorly. I might drag out of bed to ride right seat for 136 an hour too.