If you have a look at the players we had in our midfield rotation, versus the players Hawthorn had in theirs, you might be able to answer your own question.
Green, Bruce, McDonald, Jones and Godfrey were the only bona fide mids we had in the squad. The rest were kids (and Jones is still a kid). Bring the likes of McLean, Johnstone, Pickett, Sylvia and Moloney into the mix and you'll find the fitness won't be such an issue.
Conversely, Hawthorn basically had its full midfield mix out there (I can't recall seeing Vandenberg, but he's the only one).