Critics of Sword Art Online's later arcs likely dislike them because they move the story away from the only one they initially cares about – Aincrad. To them, each subsequent world that doesn't return there is worse than the last. However, by the time Sword Art Online reaches Underworld in the Alicization Arc, everything has not only already improved four times, but all of them build upon each other and view the same characteristics from a different perspective in a way that would have been impossible if the story remained in Aincrad.

https://screenrant.com/sword-art-online-anime-fourth-world-improved-over-time/