Let's talk a little about Corrin, on how much she benefited from the 8.0.0 buffs and how she compared to Smash 4 Corrin.
I think the 8.0.0 buffs are incredible. Before the patch, Corrin could often struggle quite a bit to secure kills. She had some kill confirms, but they weren't always super consistent, and her raw killpower was lackluster. All of this changed in this patch, every single kill confirm got stronger and more consistent (and kill earlier), her raw kill power got significantly stronger as well. Oh, and her damage potential is better, and pin is much safer since pin jump has a fairly low amount of end lag now (they shaved off 10 frames of endlag, from FAF 40 to 30!).
So if we look at the buffs, well... Tipper F-smash deals slightly more damage and kills significantly earlier (around 15% or so, scary stuff). Oh, and f-smash got 7 more frames of shieldstun on the tipper, and 5 on close and medium range, which makes it much safer on shield. Generally speaking, tipper f-smash will be safe on shield now, which makes f-smash a much more appealing move.
Forward-air got increased damage and compensated knockback scaling. The increased damage means more hitstun, which means better combo potential and making it more consistent into kill moves. Some common kill moves are fair to RAR bair (which got buffed and now deals more damage and kills earlier, making it a strong kill confirm), fair to Dragon Fang Shot (which used to be a 50/50 but with the increased hitstun from fair now is true at certain %), and fair to tipper pin (also true at certain %, if you react to the DI). Oh, and up-air got more damage and kill power, which makes it not only a strong raw kill move, but also a kill confirm: Down-tilt to up-air is true at some % and even if it's not true if they DI the down-tilt poorly they'll still get hit by up-air! Oh, nair into bair is also a kill confirm and since bair got buffed it kills earlier.
Oh, did I mention that aerial tipper has 4 less FAF? It does, making it possible to full hop pin and canceling into a nair or something to autocancel it and land without much lag. Oh, and pin kick kills like 19% earlier now, giving it more raw kill power (I've killed people at like 80-90% near the ledge with a pin kick).
So, is Corrin better after the 8.0.0 patch? Yes, she's greatly improved. Let's compare her to Smash 4: Basically every normal move, except for down-smash, is better in Ultimate. Fair is a bit slower (frame 9 instead of 7) but combos better than in 4 and deals more damage, down-smash's tipper is much worse at killing compare to 4 (though at least it has 5 less frames of endlag). What really got nerfed was her specials: Her up-B used to have really poor range, but it got buffed in patch and now goes noticeable further than in 4. Unfortunately for Corrin, her aerial drift after up-B is low, making it more difficult to recover high. Still, it goes further than in 4, has more intangibility, and kills earlier, so it's not necessarily worse overall (if you recover low it's strictly better than in 4). Being able to go low to edgeguard with back-air is really nice, too.
Her neutral-B got some buffs and nerfs. The bit is a bit worse, it used to be that a partial bite would kill quite early but now it won't kill as early (non-fully charged bites kill less early in general). Fully charged bite kills a bit earlier though, which doesn't really matter that much since it still kills later than partial bite. A bigger nerf is that uncharged shot no longer combos into a full bite, so you might have to settle for a weaker bite. The uncharged shot comes out 2 frames slower (17 instead of 15) and FAF 62 instead of 60, making it slightly slower.
But it did get one noticeable buff: The actual shot can now kill opponents that are off-stage, so if you charge a shot and snipe their recovery you might kill them. I don't think it makes up for the other nerfs but it's still a solid move.
Counter Surge got wrecked, it's basically worse in every way (the only upside is that the counterattack window lasts for 2 more frames, 7-26 instead of 7-24, but that's fairly minor). It kills much, much later. It has much more endlag too, meaning it's no longer that good as an anti-projectile tool. The latter aspect probably hurts the most versus Pikachu (since Counter Surge was so good against him in 4, now it's lackluster), while the former hurts against many characters. It's generally not a move you'd use much in Ultimate, going from one of the best counters to a very lackluster counter, noticeably worse than Lucina's.
And I saved the most important nerf of all, Dragon Lunge, aka Pin. Before the patch, this move was worse compared to Smash 4 pin in most ways. This patch gave it two very good buffs: Stronger kill power from kicks, and less endlag from pin jump, over 10 frames faster than before and compared to Smash 4, and pin jump is intangible from frame 2-7 instead of 2-5 (which I doubt is very significant but hey, it's a buff compared to 4). She can also pin cancel which she couldn't in 4, and this has some occasional use.
But the kick range got buffed, significantly, and it has more endlag, quite significantly as well (11 more frames for forward kick, 25 for back kick). This is the main nerf to Corrin compared to Smash 4. Pin kick is rarely safe in neutral, and usually it's safer to pin jump if you accidentally pin their shield (which, granted, is safer than in 4).
Oh, and a universal change that makes you sometimes makes you turn your back towards the stage makes recovering with bair slightly more annoying, now you have to B-reverse or side-B in order to do it sometimes. Some universal changes are good for Corrin, some are bad. Her grab is rather pathetic in this game, but at least she can pressure shields with charged f-smash (which is a fun buff, since you can charge for around 3 seconds it'll break shield or poke shield and kill them in many cases, if they can't get out in time).
I didn't go through every single change to Corrin, these are just the most significant changes. Still, when you take this all into considerations... It's not looking all that bad, is it? The main issue is pin kick having less range and being more laggy, which is bad, sure, but she got so many other buffs. I don't think she's necessarily all that much worse than in Smash 4. One big nerf, some small nerfs, lots of small bufs and larger buffs.
Overall, I think she should be close-ish to Smash 4 viability. She probably has fewer matchups which she totally dominates (since pin won't easily win neutral versus certain characters anymore), but she should still have primarily slightly winning or even matchups, with some slightly losing matchups (and potentially no really hard matchups, time will tell I guess). In Smash 4, she was generally perceived to be a top 13 character near the game's end (though parts of the community was slow to accept this, many thought she wasn't even top 20 and called her a "high-mid tier" because they didn't like that she has below average speed). In this game, she doesn't seem to be that much worse than in 4 after all the buffs. Top 20 seems very plausible, and if not, then probably top 25. She's good. Cosmos thinks top 15, although given that this game has quite a lot of strong characters I'm a bit doubtful of that. Top 15 doesn't seem 100% impossible, but fairly improbable. Even top 20 might be within her reach. She retains most of the strengths from 4, while getting quite a few new tricks and increased power, although some aspects of her special moves are worse.
Corrin is probably one of the most underrated characters by the non-Corrin mains right now. I can't really blame people because I was a bit hesitant at first for the first week of the buffs, but the more I think about it and the more I see Corrin players like Cosmos and SHADIC play her and the more I play her myself, the more I feel that she's a good character now. High tier, somewhere in the #17-#23 range probably. I don't think she's much worse than Smash 4 Corrin.