Reddit was absolutely not an image board to begin with. To begin with there wasn't even a convenient way you could even post images! Which is why imgur was created 4 years later!. Reddit 2005, Imgur 2009.

Reddit was originally 100% text based. Reddit was originally a general discussion forum, and the structure and dry text only format attracted mostly (to some degree) nerds and intellectuals, so the knowledge of users was generally above average, and so reddit became an amazing information hub too.

Unfortunately more "user friendly" design and the increasing popularity and the end of Digg resulted in more noise from users that detracted more than they contributed. When I left I estimate more than 90% of users weren't even familiar with rediquette, which laid down excellent principles for how to behave. Like don't downvote because you disagree, only downvote if a post doesn't contribute to the discussion. It was almost never mentioned, and it was clearly not followed by the vast majority.

So being a debate forum with many knowledgeable people, slowly went out the windows, so more than a decade ago it was over IMO, and the quality of posts and discussions had dropped so dramatically at that point, it was no longer worth it.

To me all the shenanigans after that point are basically irrelevant, reddit hasn't been worth it for more than a decade IMO.
Apart from that he has some good points, especially the centralized and AI parts.