I have said a few times - Sylvia, Bate, Green, Bruce, Grimes, and 'McDonald/Bennell' will run through the middle from the forward line or back line.
I think that Davey, Moloney, Morton, Jones, Sylvia, Bate, Green, Bruce, Grimes, Scully, Trengove, and one of McDonald and Bennell are enough legs to run through the middle. That's 12 players rotating through all areas of the ground and the bench. Leaving 10 spots for two rucks, 4 set forwards (Watts, Wonna, Jurrah, and one of Miller/Petterd), and 4 set defenders (Frawley, Rivers, Warnock, and Garland).
I think it's a decent compromise.
I also didn't want to see blatant poor balancing of a team to fit in as many mids as possible ie. 1 ruckman, Blease on a HFF, Davey in a FP, etc
Note: Davey in a FP is disengenous because he will spend more time in the midfield than in a pocket so it is not a balanced 22.