Since we were talking about Peach, I'll give you guys some simple input... her MUs, in my opinion. Peach's number is always on the left.
Fox - 45/55 on most levels, 60-40 for Fox on PS, 60-40 for Peach on FD
Marth - 45/55 on most levels, 60/40 for Marth on YS, 60/40 for Peach on DL64
Sheik - 40/60
Puff - 40/60
Falco - 50/50
Falcon - 50/50
ICs - I dunno. I wanna say 70/30 for most ICs but much closer if you're Wobbles (40-60) since he's actually 80x better at it than everyone else.
Doc - 60/40 (Alan convinced me, watched him in action in real life, Doc isn't that good but d-throw fair kills at like 85% so it's cool)
Ganon - 60/40 (turnips, combos)
Samus - unsure, maybe 55/45 since beam is good and so is not being comboed by Peach
Pikachu - 60/40 (shield, d-smash, basic defense, heavy hits)
Luigi - 60/40 (jabs are important in this one, as is keeping him locked down - don't pull turnips when he can wavesmash you)
Mario - 60/40 fire is lame and so is uair comboing but float back, shield, and being lame wins more
DK - 70/30 because no shield and Peach combos harder unless he can punch her somehow and turnips are lame and dash attack beats his bair too much
Link - 60/40 maybe closer but Pink Shinobi was real and Link's shield grab isn't but then again his uair is so maybe idk
I know a lot of these values seem low but I feel her speed limits how much she can shut the opponent down, even if her combat game is really tight in terms of technical data (frames, reaction windows, etc). Speed limits how much she can do it and empowers rolling and other movement defenses until the opponent gets cornered basically, which isn't always a death sentence anyway because invulnerable ledgedash by Marios and various other characters. In a bizarre way, it also limits her movement game's mixups since she only has a few ways of manipulating space between herself and the foe but that's some deep ish that doesn't belong on the boards yet =X
Anyway, for these reasons (and her combos being unreliable or non-existent in some MUs aside from maybe 1 or 2 specific things she can get at some percent), I feel Peach is not as good vs the mid tier and bizarre characters as Marth overall IMO. Marth really ***** some of them super hard but Peach doesn't but Peach's MUs with them requires almost no learning curve since her combos are all the same in every MU and there's no real percents game with her stuff. Marth is required to know a lot.
Like, I think Marth ***** Link really hard. But he needs to know when Link can be u-thrown into things (if ever), how his techs work, nuances of beating his recovery, etc. Peach just sort of floats into a pressure sequence and Link doesn't really get **** comboed unless he lets it happen (since his weight is okay for escape plus she's slow and his combo break options in the air are okay vs her) but it's hard for him to interact with it.
Same thing with like... Mario. I think Marth is better in the MU but Peach's stuff is the same stuff she does to every character.
I also tend to feel Marth has a really high learning curve though. Since his MUs all require him to modify his DD and other stuff to suit the new significant ranges and other stuff.
The exceptions to the above are basically Pikachu (who I think is okayish vs Marth and have felt this way since before Ken so don't give me that), ICs (since they've worked on this one and play it super lame), and maybe Ganon (I swear his DD obliterates Ganon and Vwins's crappy Marth has wrecked Kage many times before my eyes with basic anti-Ganon stuff but idk maybe Kage was high or something - in region is weird and has questionable validity). Anyway... I'm getting off topic. It just so happens that those three characters are piloted in high level circles instead of one of the numerous other useless mid tiers. Go figure. I think if there were more Samus players, Luigi players, Zelda players, and like... I dunno. Puffs. Then Marth would suddenly look way better (this is where smash having a tiny player pool is a drag since it limits how many characters actually get played even when there's a bunch at similar power level like the mid tiers). Or if more people just played Fox since that's what Marth's main source of happiness has been since like 2K7... eating the Fox players.
Also, this is gonna sound weird but I think more Peaches in the field would be good for him. I think this because aside from like... VaNz, Vwins, and MacD*... for a while most of the medium-high level Marths (HBK, IB, etc) beat the other Peaches iirc. It's just in the higher circles that Marth starts to lose IMO and I'm still not convinced that's 100% Marth's fault since those Peaches (VaNz, MacD, Vwins, etc) also won a lot of their locals and placed higher even when they didn't take out the Marths.
I dunno.
Maybe I'm wrong and Marth sucks. Maybe I'm right and he's good. But I really don't feel I've seen anything conclusive either way the entire time this topic has plagued the community. Maybe we should just accept it's a gray area and focus on a new one. Like Sheik vs ICs or something. I think uair is good vs ICs as Sheik. What do you think? And what about Puff YL? Is it time for Armada to learn another secondary? Or is the MU actually a fair MU? Or does Puff actually get 7-3ed like phanna's old chart would suggest? Find out on the next episode of "The Metagame!"
* Armada is obviously excluded because he beats everyone.