Mitchell has been no where near as consistent as kerr.
What? Do you even football?
Kerr had his first elite year in 2005. He backed that up in 2006 and 2007. 2008 he was injury riddled and played just 11 games. Only 11 again in 2009, averaging less than 20 possessions. Worse the year after, 4 games. 2011 he was decent but by 2012 was very inconsistent - good 1 week, invisible the next. 2013 he retired after 10 games. Kerr was brilliant at his best but never showed it consistently once Judd and Cousins left, mainly due to injuries. 3 or 4 good seasons across a career is not consistent, whatever the reason.
Mitchell on the other hand won the B&F in 2006, 3rd in Brownlow in 2007, Captained premiership (and Hawks best mid) in 2008, B&F in 2009, injured but 28 pos per game in 2010, Runner up Brownlow, AA and B&F in 2011, runner up Brownlow and B&F in 2012, AA 2013, injuries in 2014 (still averaged 30 possessions if not counting injury, won the premiership and was 1 voted off the Norm Smith). That's not counting the year he was rising star, very good in 2005, etc.
Mitchell as definitely been more consistent.