I think part of is the nature of it. Why would you get sufficiently into this scene, care enough about this one game to post video after video of you speedrunning it, to then cheat? The challenge for someone doing it manually is to do it manually; the challenge for someone doing it TAS is to do it TAS. Without the challenge there is literally no reason to do it. So while lack of evidence can't really prove anything, there really isn't that much motivation to cheat. If it was a complete nobody claiming they had manually set a record, yeah, that's suspicious, but someone well involved in the scene either is playing the long con for something that they themselves don't care about (and which they can't really revel in since any sort of in person interaction would show they're frauds), which is unlikely, or they're legit.

>Without the challenge there is literally no reason to do it.

What about money? Fame? Aren't these reasons?

And there are countless examples from history of 'the best' in whatever area getting caught at cheating just to stay 'the best'. I'm not really sure what you're getting at with this.

Actually plenty of people who have been deep in the community have cheated. It happens. But given that this run was performed live during a stream where he is reacting to chat it is pretty unlikely that he was doing playbacks of the entire stream.