I used to believe Mario was High Outerversal (yes, ik it's crazy) but I realized how wrong I was later. Mario doesn't touch 5D.
Starting off with Base Dimentio, this guy is Multi-Solar System level at best. Dimensions in Mario aren't regarded as being universe-sized. This scan proves that dimensions =/= universes:
String Theory Soup is a name fallacy btw. String Theory Soup only seems to give temporal universe omniscience as its description says nothing about "theory of strings" or "11 dimensions". And the strings in the sky have no context whatsoever so assuming that they prove string theory is assumption fallacy. I can't believe people still believe this stuff. And the "jigen" scan has nothing to do with string theory whatsoever (this claim falls under assumption fallacy as well). The guy who made that scan (Bill Decipher from Quora) even admitted this but just hasn't taken down his flawed Dimentio scaling yet. So no, the Marioverse doesn't have string theory and it's not a debate at all.
And btw, Dimension D resisting The Void isn't a reliable claim. We never saw The Void in the background of the Underwhere:
And The Underwhere is located just below The Overthere. But The Void was still active in The Overthere.
More proof for that Dimension D never resisted The Void is that there were a few dimensions (like The Bitlands) in Super Paper Mario which weren't underground and appeared to be unaffected by The Void (likely due to the fact that The Void had not begun to consume those dimensions yet; as Merlon stated that The Void would grow to consume all surrounding dimensions). This could have very well been the case with Dimension D. Considering the fact that Dimentio created it in The Bitlands.
So all this proves that Dimension D has no transcendence over The Void.
As for "Base Dimentio surpassing The Void" claim, this post made by another user solidly debunks this. (Although Mario tanking The Void is a Universal durability feat, not a Low Multi feat; as I've explained that The Void had only consumed the universe's mini-worlds at that point). Most of the claims for Base Dimentio matching The Void fall under assumption fallacy and Dimentio didn't even kill Mario and the others, as confirmed by Queen Jaydes:
So now all of that is out of the way.
From what I've seen, the universes in Marioverse have no space-time continuums anyway. So Base Dimentio is Multi-Solar System level (due to creating Dimension D, which had a few constellations). And Super Dimentio is only Universal+ level due to Matter Splatter Galaxy being a hyperspace, which refers to higher dimensions (making it a 4D structure):
Final Scaling for Base Dimentio: Multi-Solar System level
Final Scaling for Super Dimentio: Universal+ level