Yes, there's also the D-League, but the team has a lot less control of the minutes their players get I believe. Sometimes it's better to have them roll with the club and practice with the team.
Except that Butler is younger and has a career wRC+ of 117 (last year an anomaly for him) and is projected for 119, while Navarro is a career 86 wRC+ projected to be a league average hitter, and is, miraculously, slower than Billy Butler.