Not true. I only went back the last six years but here are the Conference RPI rankings for the MVC, CUSA and Horizon leagues (in reverse chronological order):
MVC: 9, 8, 6, 4, 6, 7
CUSA: 11, 10, 11, 14, 15, 9
Horizon: 14, 11, 9, 10, 14, 18
The MVC is clearly far better than CUSA and...