Ooooo, yeah, that's not good.
You can do Let Coach Decide with a partial blank (only 1 position filled in), and that'll usually work fine for training. I've tried doing Let Coach Decide with PG spot filled in between 2 players. End result was bad. Starter got like 44 minutes, backup barely played and didn't really even sub in at SG.
My Utopia team recently did Coach Picks from Depth Chart with full roster set...that also didn't spread minutes out at all.
Seems like the only two settings I can find that do anything are Blank (or partial for 1 spot and 1 player only) with LCD. Or Strictly Follow with Starters/Backups fully filled.