Going back to 2013 the Bills have ranked higher than 29th in Pass Percentage once (2014), you have to go back to 2011 for them to be in the top 10 (7th) at 60%. I don't think the stat alone helps that much in determining team success, because it can be affected heavily by the need to throw or grinding out games you're running away with. Last year The Pats, Rams, Saints Bears, Texans, and Ravens were all in the bottom 3rd and still made the playoffs and two of those teams were in the superbowl.
However, the bills being 29th or lower every year without that kind of success is more indicative of outmoded style in my opinion.