I watched the GGO part of SAO II because I was in middle school, but I watched the Mother's Rosario arc last year (2021) because I heard it was pretty good and let Asuna shine and didn't have Kirito in it at all. I really love Asuna, and I think this arc does her the justice that the rest of the series was unable to so this is a review of JUST the Mother's Rosario arc because that's the only part of SAO I actually care about even a little bit.
In SAO original, we're repeatedly told that Asuna is Kirito's equal in battle, but we're never shown this and there's never been an opportunity for their skills to really be compared. The arrival of Yuuki, someone who was able to beat Kirito, gives Asuna an opportunity to show these skills that we've been promised, and she absolutely delivers and it was the highlight of my month. Mother's Rosario is a redemption arc for the SAO writers. Where SAO original fails to adhere to its theme of digital relationships and experiences being just as important and meaningful as real world ones, Mother's Rosario is the perfect plot for it.
Yuuki feels like the character Kirito could've been if he was written well. She's the same kind of overpowered, way-too-good-at-video-games, obviously an introvert and a social outcast character that Kirito is, but this time with heart and purpose. She has a goal that's more than "I wanna play video games because society SUCKS and I don't get along with people" and for her especially, that goal means something more than being able to say you're really good at a video game.
Yuuki also works because she has friends. If you want to write a story about digital relationships being important, why would you make your main character stop caring about people, and why would you make the relationships they do eventually have exist under the pretense of them all being girls that have a crush on him but just follow him around because he's dating Asuna. Emotionally, Kirito is so disconnected from the entire cast, but Yuuki actually cares about her friends and is able to connect with them because they share a struggle.

Spoiler, click to view

The entire cast being physically disabled people is incredibly important for the theme, as it makes it hit home that much harder. For Yuuki, the only relationships she can have at all are digital ones. It's her entire world, and it's just as important for her as real life relationships are for other people, and having her guild's name on that plaque is a way that she can leave a mark on the world that's means something to her. It has meaning because she gave it meaning, not because it's just inherently important because it's not. It's a video game, why would it be all that important? But then the whole point of the story is showing the audience that these things can have meaning for some people and shouldn't be written off just because it's in a video game.

Other than Yuuki being a great character and the plot being one of the best vehicles for a theme I've ever seen, you also get to see Asuna actually fight for the first time since checks notes she met Kirito. I can't actually remember a single time other than that first bull fight that we get to see Asuna do more than walk into a dungeon with the rest of the cast and then watch Kirito beat up a monster. If SAO disappointed you and you wished it was better, just watch the Mother's Rosario arc.