I dunno. I tend to look at losing matchups as being one of two kinds. The first kind is the sort of losing matchup where one character has a strong edge over the other due to the fact that the winning character's tools force the losing character to play more carefully, or more precise, or at a higher level in general. A good example of this I think would be something like Ness/Samus. Samus is near-ungimpable, extremely difficult to kill and combo, and can wall Ness out very successfully with projectiles. As such, Ness needs to be extremely cautious and spot on. He needs to shield and avoid projectiles, not overextend his combos to leave himself open for punishes, and take his own punishes where he can get them. Since she lives so long compared to him, he needs to outplay her many more times than she does him in order to secure a stock, so while he's doing all this he needs to get hit as little as possible. These are things that are difficult to do, and that is why the matchup is considered bad. But if Ness is on his game and can do these things, he can win. So the matchup is not a total loss in terms of character viability.
Then there's the matchups where the edge that the winning character has over the losing character seems to go beyond simple precision. I think Bowser/Icies is a good example of this. Icies have every conceivable advantage over Bowser. He's a tremendous target. Desync ice blocks and blizzard in the neutral are very difficult for him to get around without Bowser getting clipped and taking free damage. The desync walls tend to force Bowser either into the air, where he has no reliable descending offensive options against Icies and can easily be intercepted by an utilt or uair, or they force him into the corner, which is bad news for any character but especially bad for Bowser. If Bowser does get in, he doesn't have much to go on, because his attacks are pretty slow and Icies can essentially shield everything because next to none of his throws are all that great at separating them so grab is a nonissue. Not only that, but a grab from Icies almost anywhere on the stage will kill Bowser at pretty much any percent, considering the fact that he's simply too big to reliably escape dthrow dair midstage and any grab on a platform or near a ledge essentially kills him instantly because the dthrow/fthrow handoff is an infinite on Bowser. This goes past Bowser needing to play at a higher level than his opponent. Not only does he need to play so that he is never touched, he doesn't have any reliable tools to touch Ice Climbers. He will get hit at some point. An Ice Climbers player who knows the matchup will, in my opinion, have a huge advantage over Bowser, by a wider margin than most bad matchups. I mean, disclaimer, I'm not saying I could beat Odds here (the skill gap between me and a Bowser player of that caliber makes matchups almost irrelevant, because I suck). But I feel safe assuming a Bowser main would be so much better off counterpicking anyway, because they could avoid so much unnecessary grief doing so.
I'm just spitballing here, really. I could be wildly off in my analysis of what actually makes matchups bad. I also could be evaluating the second kind of losing matchup based on the same factors and characteristics of the first kind of losing matchup without realizing it. But I guess what I'm trying to start a discussion on is, how many bad matchups are the first kind and how many are the second kind? I can't think of many that are the second kind, but I'm not nearly as knowledgeable about the overall matchup spread of this video game as I'd like to be and I was looking for the input of some more well-versed players.