I don't get where we have the notion that "the lowliest of Minions" in a verse with superhumans out the wazoo somehow makes Goombas amd the Minions superior to them merely "Wall level". I also feel like they SHOULD scale to their speed feats and reaction times as some Goombas can attack Mario and Co. and legit react to them as far as Super Mario Odyssey and as early as New Super Mario Bros. or Galaxy. Amd while Mario can gain control of a Goomba, if their body's weren't capable of sustaining as low as an MHS+ character, then Mario would literally not be able to react to anytbing as a Goomba mor have a use for their transformation. Mario transforms into things and gains their attributes and abilities, and the fact that same game has him traversing and maneuvering as electricity from a power line as well as him not having any noticeable stat boosts while in other forms unless they're just >> other transformations for obvious reasons like a Chain Chomp's physiology or Bowser himself, then I see no reason why we have these made-up tiers for them when they SHOULD logically scale to the lower-ends of the verse, which even then amongat the spin-offs and main canon have hypersonic and at least building to city block level characters.
I'm glad the residential Mario guy agrees with the Power Star rating being stupid when Mario legit has never actually utilised Power Stars to boost his AP in canon and the very nature of their abilities is counterintuitive since a Base Mario, Yoshi, and Wario can beat supposedly amped characters with these things as well as Bowser having magic that needed a good quantity of those Power Stars he actively hid away to dispel its effects. Bowser might have had the Big Power Star, but in every other fight, he merely drops a key that unlocks more of the castle and if he DID have that Big Power Star then, then that means Maeio even with a smaller quantity was still above a supposedly amped Bowser yet STILL needed more to revert the effects of Bowser's magic. None of it makes sense.
Also, unlike Link, where most of his explanations come in the form of him gaining stronger abilities as he grows alomg his journey, most Mario games don't have such a story and typically have all characters at their casual bases, to which even if you argued early game RPGs, they still have building to city block level feats.
As far as universal characters? Dreamy Bowser, if you don't try and mix canons and elements from Mario Party into the RPG that literally retcons that game's source of dreams DOES have at least MSS stats considering the backgrounds of the dreams had stars and constellations while the Giant Battles have Luigi literally jump high into space. Using the displayed sizes of the dreams from the source allows it to fall consistent with 4-A ratings. King Boo, Black Jewel, Bowser in 64 and the whole "Mario characters beating amped bosses in base who were powered by things that supposedly could create dimensions with entire star systems", some of Paper Mario's attacks in Paper Jam, the Solar System feat in Galaxy, and likely more.
For actual support towars the OP's post? We have Culex, Dreamy Bowser, Megabug, Bowser wanting to do his shenanigans in Mario Party like destroying all dreams or something like that, his vague survival statement from the Prima Guides, Rosalina being constantly said to "hold her own" with the heavy hitters of the series in spin-offs with her "cosmic powers", the Grand Stars being the reason Bowser's machine malfunctioned and devoured the universe, Lumas being comparable to Power Stars supposedly of which Mario has shown he doesn't need them to beat characters powered by them, the black hole in MP effecting the galaxies in the background supposedly, the Sammer Kingdom thing, and likely more.
But my word isn't likely to be taken with any merit.