I'm just going to say it, Adventures of Link is objectively a horrible fucking game with apparently no direction. I've sunk 50-100 hours on the original Zelda. Maybe 5 on the sequel? 4 of them trying to find a silver lining.
That's a bit heretical if you consider the context in which SMB2 came into being. It introduced many new concepts not present in the first SMB and stands on its own. It isn't just another side-scrolling platform, it was also way more vertical, way more scene transitions within a single level, the ability to move context between intra-level scenes, multiple playable characters, each with different abilities. It certainly influenced future SMB games (SMB3 implemented a similar-if-you-squint slot machine mechanic at level end). Similar to Zelda 2: The Adventure of Link which was also dramatically different from the first Zelda and it too influenced future Zelda games.
The argument that it's not a real Mario game is a bit silly really. There are long standing pieces of Mario lore that came from Mario 2. Luigi being taller and more slim, Peach being able to float, shy guys came from Mario 2 and they are a staple enemy in certain other games and Yoshi games.
It isn't just a reskin, there are a lot of differences. One of the biggest is there is no run in Doki Doki. That makes the experience extremely different from the running and jumping action of Mario.
The level design is fantastic. The original Mario Bros. 2 feels like a romhack of Mario 1 designed to troll you. It's like the final boss of Mario games.