So I guess you've changed your mind in the last month or so?
I guess my view is outdated. And it's likely I haven't played a good Mario. I've not had one pressure me as you say they can.
I'm not offended about Mario not needing secondaries. I don't believe secondaries are based on the characters, as much as I believe they are based on the person playing the characters. Most people, myself included, can't play a character to perfection in every MU to not need a secondary. That's just my opinion.
Regardless, I'm not here to discuss Rosalina's MU, but more of the Pikachu and MK MU. Do you have any advice for those?
I just want to say that I didn't mean to come off harsh. Sorry about that. Also, what I said a couple months ago was a bit outdated even then. At that time, I was paying slightly less attention to the meta than usual.
As for the Pikachu MU, it's a pretty solid 60:40 in Mario's favor. As an example, ESAM himself said that he needed a secondary just for that MU. Quick Attack, one of the main/only moves that keeps Pikachu relevant, is utterly destroyed by Mario's U-smash, since it gets caught in it as Pikachu tries to move around the stage with it, netting Mario early KOs. This means that Pikachu pretty much can't use it offensively in the MU which is huge. Another thing is that Cape destroys Quick Attack, as well, by reflecting it which can net super early kills, forcing Pikachu to be even more careful with using it.
TL:DR Pikachu's Quick Attack (the most important move he has) gets trashed by Mario. Also, Pikachu is pretty easy to combo and dies early.
In the case of MK, I have less experience with the MU, but I will tell you what I know. Currently, I would judge it at 55:45 to 60:40 in Mario's favor. MK has no combo breakers, relatively weak air speed (too weak to escape Mario's combos, at least), fast falling speed (which makes him even better combo fodder), very light weight, and no longer has a quick kill combo that can make Mario play careful. So, pretty much, you have a character that Mario can feast on with his combos and that he can kill super early. What MK has over Mario is amazing edge-guarding and a top 3 recovery.
So, overall I would say it's maybe a strong 55:45 in Mario's favor or a weak 60:40 in Mario's favor.
I hope this helps you!