I WIN.
Wait. Forged evidence. Right. Looks like I'll have to do this legitimately.
My evidence this time around is the hole in the upper right corner of the image. It's based off of one that Ridley makes in Other M. It lends Ridley a connection to the stage that Mother B. lacks. I don't see a large glass tank in the arena, do you? It's pretty clear that this stage is a recreation of the one in which you battle Ridley.
True, there have been cases of stage hazards appearing where they shouldn't. But there has been reasoning behind it every time. Cresselia appeared in the Spear Pillar stage alongside Dialga and Palkia. Dialga and Palkia still appeared on the stage; Cresselia was just a bonus. Dialga and Palkia were still there, so my point stands: Ridley should be tied to this stage (whether this is his playable homestage or he'll be a hazard here). Maybe Mother Brain is a bonus, but that doesn't change that precedent states Ridley should be the main course.
Kraid's stage in Melee (Brinstar Depths) is as you quite nicely put it: "resembles nothing of its origins." It is NOT a recreation of the Kraid battle area! That makes it completely irrelevant in this situation, as this case deals with a recreation of the area where a major character appears.
I will concede, however, that Mother Brain is an enemy who may be considered a "trauma" to Samus. However, picture that was posted alongside the quote strongly suggests Ridley and in no way suggests Mother Brain. If it were just the quote, you would indeed be correct. But ignoring the secondary piece of evidence, Mr. God Robert's Cousin, is quite unprofessional.