You know, you're quite right about these blokes. They are all below par as far as disposals go. The only one I'd care to argue with is Polo, who actually showed some very good skills and creativity in certain games off half back this year. The stats back your assertions up quite clearly though:
McGuane - % effective 77.3, % turnovers 13.8
Polo - 76.1, 10.8
Jackson - 66.4, 11.7
White - 70.8, 14
For comparison's sake - Yablett 78, 8.7 / Goddard 76.4, 10.1 / Gilbee 74.5, 8.7 / Boyd 72.8, 7.5 - are all significantly ahead of our guys (apart from Polo) statistically.
The only thing that might be worth considering is that the teams these guys play for are good. They have structure, good game plans and most importantly their teammates work for them. They shepherd and block to give help create time to dispose effectively and they work hard to create options all game long. Perhaps if our team can start to do these things some of these guys will look better than they have. Apart from Jackson none of them really have any trade value and there are plenty to go in front of them so it seems pretty likely we'll see them running around again next year.