Mamoru functionally transforms from one suit to another suit. The cloak doesn’t even bother to change. Yes, just as well you did that then.
What’s even the advantage of him going into Endymion-mode? Just a better link up for Usagi-in-Serenity mode maybe? I just find it kind of funny that for all this he basically just got a sword, which isn’t exactly useful here unless he’s planning to hack a path through the atmosphere.