Rumors seem to be all over the place right now. Sounds like both are at fault and Platinum couldnt deliver what MS wanted and the Studio was probably in way over their head. They released a few games when this was announced and still have a game coming in early 2017. they have like 193 employees and thats what I expect for developing an open world game.
But apparently Platinum couldn't deliver what MS wanted because MS was setting intentionally impossible milestones to work around the contract
The exact same thing happened with Phantom Dust.