The Baltimore Orioles (2011-2012), Cleveland Indians (2012-2013), Pittsburgh Pirates (2011-2013), Boston Red Sox (2012-2013; ok they are not mid-market), Detroit Tigers (2005-2006) will disagree. Lots and lots of examples of rebuilding in a season or two, but they all required drastic change of FO and field management personnel. If you don't do that, you cannot rebuild in 1-2 years. That simple.