As was feared people are throwing games in flex role just to get passes, so I would suggest that the flex role should only reward wins (let's say with 3 passes), and even take away priority passes for losses (let's say 1).
Because if you're an average tank main like me, then you'll win half your games, and play a lot of them (I don't bother with dps if the cue time is more than 4 minutes). That means you're constantly at max passes, waiting for a time when dps lines are short.
.....
