The main thing is post more. Lack of content is the main reason people don't use Lemmy more, and the only way to fix this is to share/produce more.
Its a bit of an unpopular opinion, but I think even (transparent, community-relevant) bots are a good idea at this point, given that 99% of interests have little to no activity currently. For example, if we had bots that post game update changelogs to their relevant communities, it would at least provide a baseline amount of content and make it easier to discuss for fans of those games.
While I think he's overreacting a bit, I could absolutely see how he'd come away with that opinion. I mostly agree with him, as a broad assessment of Lemmy.
In terms of content, 90% of whats active is politics. That leaves like, 10% of the already small content pool for users who aren't interested in it. At the same time, this lack of content (and lack of users) centralizes content in just a few, broader communities.
In terms of his assessment of users, I could definately see this too - esspecially in the bigger communities he was likely pushed towards (by the lack of content). Lemmy does have an elitism problem, both on the tech side and esspecially on the politics side. Making it even worse, there's a pretty good chance he ended up on .ml or one of the worse tankie instances, or at the very least, was frequently interacting with them due to their size and activity. If he didn't immediately block the tankie instances, I'd be more suprised if he didn't come away with a negative impression.
In terms of mods, it'd depend a lot on which communities he tried to participate in, but again, I could easily see how he'd end up having this experience. Even ignoring the massive presence of totalitarian bootlickers on Lemmy, as I previously said, the lack of content causes things to centralize. In theory, you can split off to your own communities, but in practice, its nearly impossible unless a mod simultaneously pisses off the whole community at once as happened with 196. Even then, the community needs to be quite large to jump-start the competing community. Until Lemmy gets large enough to have multiple communities running in parallel or for new communities to quickly and easily grow, mods will continue to be a potential problem.
All that said, I'm still here. I think, despite its issues, Lemmy has a much stronger foundation. Unfortunately its still missing most of the rest of the structure (or rather, content) needed to compete with other platforms.