Upper management long ago gave up on removing poor leaders. The place is littered with marginal management (centered around director level) that don't live up to the Agios hype and don't direct the company in any meaningful way. There are some stars in this class and these are the rare directors that have risen through the ranks and not left the company for greener pastures but unfortunately they are the minority.
My greatest fear is that Agios will be another Amgen coasting off an early success that is largely driven by some early hard work and good luck with IDH (and maybe from the clever repositioning of early PKD drugs) but will flounder for years with the vacuum created by most of the early leaders and pioneers having departed. Fingers crossed that I'm wrong and things will somehow look up.