i don't like the implication that corrin is one-dimensional, a one-trick pony with pin. this is just blatantly untrue; corrin has a number of effective options and pin is far from the only thing you have to worry about and contend with when facing corrin in neutral. corrin is one of those characters that has a very complete set of tools to shut down all of your ways to get in on her. her neutral is essentially played through use of tricky movement and setups, which are so effective because, even if you know every gimmick, that doesn't mean there is a straight forward answer to it. you jump around in neutral, utilizing a combination of empty hops and spaced fair/nair/bair to condition shield. when you use full hop/double jump though, that's where the real tricks come in. corrin does a very good job at being able to threaten an attack without actually using it because of pin and her highly effective falling nair, which is hard to punish in most cases unless you are in shieldgrab range. this highly effective set of options is complemented by a fairly solid dtilt and jab, as well as dfs which is a decent projectile and absurd air dodge trap, fsmash for other ground game, and dsmash for dangerous oos punished. she can bait you into scenarios where you get hit extremely effectively because you think there's an opening, but then corrin still has the time to cover herself. a lot of the things corrin does are very safe and tricky, which makes the defensive standpoint to the matchup that people think is effective generally ill-advised. there's also this idea that corrin can't approach, something that is blatantly untrue and ignorant of how the character can exert positional pressure and utilize her offensive options.
another thing is that i don't think people realize how threatening of a character corrin is to fight. she kills sub 100 off ledge coverage (fsmash, pin, dfs) and generally has a lot of ways to catch you, especially if you ever air dodge because dfs bite is so strong and if you ever get caught by dfs because tipper pin kills so early. in general, especially because of pin but other strong options as well, corrin is very scary to fight and has her own share of jank. corrin can also get a lot of good damage off hits, especially with platform extensions, and can frame trap air dodges effectively because of nair. up air is also a ridiculous juggling tool, and you have bair/pin with range to catch people while they try to land. there's a lot to worry about while playing neutral because of random ko options and a ton of pressure in disadvantageous situations.
flaws people commonly cite (other than laming out corrin which i already addressed) include poor disadvantage state and mobility. for one, corrin's disadvantage state is far from bad. nair does a lot as a fairly quick option with a lot of coverage. it's the type of option that can force you to go for resets while comboing corrin, which reduces what you can do. it's especially effective because it is a very rewarding move to connect. dair also exists as a landing mixup. it's not perfect and a couple characters can still juggle you (basically just rosa and cloud), but landing vs most characters is not that hard. the ledge situations are a little odd in some ways, but having access to pin, jump->land with nair or dair, and ok ledge hop options makes it manageable. corrin gets ledge trapped, but not more than any average character in the cast for sure and certainly less than some of the characters considered top tier. people will also talk about recovery as a huge flaw, but anyone who has really played the matchup knows that gimping corrin is realistically hard. you have to be very precise because corrin's up b hitboxes are insanely good. her up b can be gimped for sure, but people act like every character can just get edgeguards on her like it's something consistent, which just is not true.
in terms of matchups, i think it's definitely worth noting that corrin's matchup spread is just better than most other ~11-20 characters on the tier list. at this point, diddy is only considered to have a slightly advantageous matchup by virtually every relevant corrin player. cloud is considered to be at a very slight advantage. sheik has a slight more relevant advantage, though it's still not huge, and bayo/fox also win. every other matchup is even or better, and every losing matchup is doable. corrin is commonly considered to beat mario, either go even with or beat sonic/rosa/mewtwo, and go even with marth/zss. the character's matchups vs many high tiers and mid tiers tend to be very solid.
the relatively low representation of corrin at top level atm tends to confuse people about corrin. there's SO much misinformation about this character, which is why when people see a top player rank corrin highly (because they have played with very good corrin players that show the character's best attributes) they don't understand it because they don't even know what good corrin looks like. watch earth, please. watch cosmos, ryuga too (though he's not quite as good as those two), yoc, frozen. leo's corrin that he used at the arena is also solid, as well as the japanese wifi player lc, and vivid. when people say things like 'poor/linear neutral', 'bad recovery', 'no landing options', 'loses to lame/campy play', and 'few good moves', i think it just speaks to not knowing the character.
i consider corrin an easy pick for top 15, could be top 10 in the future but definitely top 15. i really do not think there is an argument that 15 characters exist with better matchups than corrin to merit placing them above and dropping corrin lower.