People still think Corrin vs Fox is horrible for Corrin, despite SHADIC beating Light twice in a row in 3-1 set victories. Head to head can help determine how good/bad a matchup is, and I think is what is most important, but it's not everything.
Head to head is almost the least important thing, at least to me. What happens during the match can tell you a lot about a matchup, but the actual end result of a set between two top players has to be qualified, since at top level, many other factors besides the matchup determine the outcome.
It's hard to even judge relative player quality, let alone factor that quality into matchup assessments. sparg0 might be (marginally) better than SHADIC, but it's clear that SHADIC is better at playing grand finals sets right now than Sonix is, so the same logic can be applied to cast doubt on the implication of SHADIC's victory today.
In the end, even slight differences in comfortability and razor thin margins of matchup knowledge can swing results pretty wildly.
What doesn't change as much though is interactions. Those are static and easy to look at. If I see Corrin ledgetrapping Joker for 30-40% consistently and the Joker players are doing everything they can to get off ledge, that tells me that the matchup is winning or even for Corrin. That's what I think we should be focusing on.
If you
just go by results, then I think Corrin isn't just top 10, she's clearly a top 3 character, if not better.
Think about it this way. Each of the perceived top characters have multiple top reps, and each of them seem to be struggling in similar matchups -- except Corrin and Sonic.
Steve mains are struggling with the top Clouds -- acola with sparg0, Onin against sparg0 and almost every pocket Cloud from another top player has caused him at least some grief.
Game and Watch mains are struggling with Rosalina so much so that Miya won't even play it any more and Maister tried Cloud against Dabuz today.
Who are Corrin players struggling with? Really, no single character is giving Corrin issues right now, unlike every other top character other than Sonic. Diddy Kong isn't even a valid pick for this because although SHADIC has lost multiple sets to Tweek, Neo beat Tweek at Smash Con and then Tweek didn't even bother going Diddy the next time they fought.
At these events, SHADIC is beating everyone and Neo is beating everyone else. Today's Corrin isn't just even with Game and Watch, Sonic, and Steve -- today's Corrin also beats Fox and Roy (see: SHADIC vs. Light and Kola and the way he's playing those sets); she beats Samus and zoners (see SHADIC vs. every Samus player, like IcyMist and Yaura); she beats heavies and whiff punishers.
The only negative matchup we have real hard evidence of is Cloud (and I would suspect we'd have some of Sheik and Snake if we saw those matchups played more even in today's meta).
Going only by top-level, modern results, Corrin's a top 3 character in today's meta, competing with Steve and Sonic for the top spot -- more than 2 reps in the top 20, almost no losing matchups, winning matchups on most of the cast, consistent ledgetrapping and juggling and edgeguarding with a solid recovery to adapt to most unfamiliar matchups, flexibility on stages (great on FD, HB, SB, BF, and PS2)... Corrin's currently in contention for best in the game, and there's really no debating that.
Personally, I do think that top-level, modern results are barely relevant to the long term (look at Byleth, at Joker, at ZSS, at Mario), but if we're going to talk about that aspect of Corrin, let's not focus only on Game and Watch, Steve, and Corrin -- the Corrins are winning
all of their matchups, not just those 3. It's confirmation bias to focus only on matchups we already thought she won.