A reasonable portion of this episode was unfortunately spent buying time with basically every trick in the book, from struggles that don't go anywhere, to cutting away for fairly lengthy scenes happening around the robot battle during which the robot battle does not advance at all, to what I think of as post-Eva style angsty stuff - Mazinger can't fight because they're in the middle of town and quite a lot of people have already died horribly when robots crushed the buildings they were in. I can see Go Nagai doing something like that, but I suspect there would have been a less respectable tone to it.
So the episode wasn't quite up to the astounding standards the earlier episodes had set.
But it definitely picked up towards the end.
Grandpa apparently has a back up command center in the Shinto shrine, holographic images projected out of the Bodhisatva's eyes, and the 1000 armed Kanon furiously operating dozens of machines behind him.
Oh, and samurai dude is awesome.