'Metal Gear Rising' bosses deemed too much like traditional 'Metal Gear' in design and behavior, replaced with "frenetic action" bosses.
In an interview with the Official PlayStation Magazine UK, Kojima Productions producer Yuji Korekado discussed the title's state just prior to Platinum Games involvement. “Just to brag a little bit about our designs, we believe that the bosses we created for Metal Gear Solid: Rising were probably some of the best in the series, but (Keiji) Saito (Platinum Games Director) came in and said, 'We’re not going to use these bosses.' So you’ll not be seeing them this time around.”
Keijo Saito, speaking in the same interview, elaborated slightly on the shift in boss design for 'Metal Gear Rising: Revengeance,' "The boss battles and the bosses in general were completely different at the time. There were a lot of stealth concepts that were [being done] internally at Kojima Studios. Now that it’s an action game we had to revamp that, and Platinum Games provided a lot of input and a lot of ideas.”
When a troubled project changes development houses, there can often be hesitancy when it comes to disregarding advanced development. Discussing the two studios approach to gameplay and towards collaboration, Satio said, “we believe there’s a lot of flexibility for both sides. Boris was included in the initial Kojima Productions concept, and is included in Revengeance as well. We did, of course, look at [the initial version of the game] and refer to it, and there are some characters we reused from the original concept. Ultimately, the most important concept that we needed to stay within is the Metal Gear world.”
Source: OPM UK