I understand the concept of what you're saying, but if Bo is fired, it's not for what he did in 2008-2010. It's for 2011-2013. Similarly, if a new coach is hired, his progress wouldn't be measured in comparison to where Bo had the program in 2009. It would be measured with where he had the program in 2013.
What about what EZ-E wrote above didn't happen as recently as last season? And this season is only half completed.