Super Smash Bros. Ultimate is currently on version 13.0.01, so it's received no shortage of support from Nintendo. From new characters, stages, music tracks, and dozens of balance patches, Ultimate has been well monitored by the developers post-launch - in all except one area.
Ultimate's online play has long been a point of contention in the community, especially among pros who want to hone their skills against human players. Unfortunately, players are still experiencing the same lag and disconnects that they did around launch, and with support now slowing down, it looks unlikely that this will be addressed.
"Matches still stutter and lag[...]and you still get banned if the other person’s connection is terrible", says disgruntled fan Asad_Farooqui over on the Smash Bros subreddit. "3-4 player matches are basically a non-option and the input delay across every match can vary wildly. It’s a little sad to see that Mario Party Superstars has more stable online than this game after so many patches".
Many other players agree that online play is still in a sorry state. "Well they did have a patch that improved the wifi in 1v1, and then they extended it to matches of less than 4. But then a subsequent patch made it worse again, and it wasn't addressed in the patch notes either", replies brooketheskeleton.
Many are hoping that the next Smash game will use rollback netcode - something which a Smash Bros. Melee mod, Slippi, has had for some time. This would make online fights much smoother than they have been on official products. It's being pointed out by others that this would likely have never been an option for Smash Bros., since getting it in games post-launch is a big undertaking. It took NetherRealm several months to get it working in Mortal Kombat X, and considering Smash has a very different audience, it was likely never seen as worth taking up the team's time while they worked on new fighters.
Ultimate's issues with its online have been so notorious that one of the selling points of Nickelodeon All-Star Brawl was that it would be an improvement. The developers boasted having implemented rollback netcode and it quickly got the attention of long-suffering Smash fans, looking for a smooth competitive experience.