The percentage of uptake is irrelevant. If your goal is to pursue a command at JQ, then it is only the rate of offer of commands that really matters. 115 in 2.5 years with no fleet expansion (but certain expansion just around the corner) suggests to me that if a command is your goal, the timeframe will be significantly less than your estimate.
Once in however, maybe your goals change and like many, you elect to remain on the 787 has so many have done. Couple of 320 captains have even bid back to Fo's on the WB, as I'm sure you're aware.
Shrug.