Oh shit, SMB2 ain't easy. I wonder if I could tolerate watching that. Has anyone even watched it? (Why does no one speedrun the Super Mario Advance version? controls or physics fubared or something?)
Is it actually remotely competent? although I guess any retard can spend 10000 hours doing some stupid dog trick and get good enough at it.
Well, in case you weren't familiar, it's not the Japanese SMB2, known in the States as the very hard Lost Levels. It's the American SMB2, which is a much easier game.
As to why nobody runs the SMA version, I'd say it's likely due to a couple factors. First, it's probably been harder to record GBA games in general (or any portable games for that matter), having to find a way to output the video to prove your run is legit. Emulation exists, but isn't always perfect. It's gotten easier in recent years, but that would still put a damper on many people's attempts. Compare that to a console game that you can hook up to a capture card easily.
SMB2 is also, naturally, a lot older than SMA, and thus more well known. A lot of people probably forget it even had a GBA port, especially since it came out as a launch title for the system and was later overshadowed by the ports of the more popular games. People would probably rather stick with speedrunning the version they're familiar with instead of picking up a new version that probably has some subtle differences. What those might be, I couldn't say, because I don't have nearly enough autism to dig any deeper.
As to whether John's run is competent, it's...adequate, I guess? It's a few seconds faster than his previous Peach-only run on the Super Mario All-Stars port of SMB2, but considering that the fastest time across all versions is over two minutes faster, there'd certainly be room to improve. The mod beat him by almost thirty seconds in the GBA version, so he's got a ways to go if he wants to get his pathetic little crown back.
So yeah, if John wants to waste hours of his life trying to play through a video game a few seconds faster, all for some semblence of self-satisfaction, whatever. He'll never be able to actually hold a record without a dozen asterisks after the fact, no matter how much of Frank's money he blows on expensive hardware for that frame-accurate experience.