I've already talked about Mario vs. Doc a few pages back so I don't really want to go into much depth on this topic. I'll address some major points of contention though
Mario and Doc's match ups
I would like to point out that there are only five MUs where I think Doc loses. They are Falco, Marth, Sheik, Falcon, and Mario. Doc does better or the same than Mario in every other MU.
My belief is that Mario performs identical vs. Falco, does better vs. Marth (still loses though) and goes even vs. Sheik and Falcon. The rest of Mario's MUs vs. viable and mid tier characters are even.
I could list specifics, but the general reasoning for Doc having losing and winning MUs is because he isn't well rounded; his single hit game is well above average and his recovery is well below average. He has more opportunity to exploit and be exploited. Mario, on the otherhand, is so overwhelmingly average that this isn't the case.
Grab games
If we were to simplify their grab games, Mario has the better low percent grab game since his dthrow and uthrow don't scale as high giving him more combo and cg potential. Doc's grab game is superior at high percent since he has the reliable fair set up and stronger fthrow/bthrow.
The problem with emphasizing their grab games as a matchup determinant is that you're implying they have a reliable way to
get grabs. Their average mobility coupled with a shameful grab range gives them little leeway to approach with grabs like Marth, Falcon, or Fox. Their bait and punish game is essentially the same and generally dependent on opponent skill so it ultimately comes down to their ability to lead
into grabs. I would say both characters rely on aerial>grab and jab>grab tremendously. However, Mario's jab is objectively better and his uair, fair, and bair are all safer on shield and the latter two are superior lead ins for grab to begin with. Couple that with Mario's ability to perform grab follow ups from utilt at low percent or usmash grounded fast fallers, he has more options to connect grab.
So even if you find Doc's grab game "better", Mario's is technically more reliable by virtue of the fact he has more ways of landing grab
The combo game
Mario's combo game is better because he has more combo openers and combo moves than Doc. Compare the capabilities of moves such as Doc's utilt, fair, and bair to those of Mario's. The changes are actually quite significant in regards to each move's respective utility. In a game like smash, you need reliable launchers to start combos. Since the combo capabilities of Doc's utilt and usmash are most reliable when the opponent is already
above Doc, his best "ground" launcher becomes grab which can be extremely hard to get. Doc is better off converting stray hits into edge guards.