So… Reddit?

I don't know, I just shared agut feeling while reading the OP. And I'm not saying it's what we should thrive for, just sharing that gut feeling about what, like I said, I consider a critical issue on Lemmy.

With the cancelled third-party apps, the visible ads, the ads hiding as posts, the powertripping mods (but unpaid as well), the algorithm trying to get the most “engagement” by showing hateful content?

That's a whole other discussion imho. But if you want to discuss about that:

• I only talked about a centralized system (aka, a unified one) and, once again, I did not say it was the solution only that it felt like that while I was reading the post. As far as I know, centralization does not imply the obligation to rely on algorithm (and ads, paywalls, or nothing dirty like that).
• As far as mods abusing their power is an issue (it is), I think we do have a few on Lemmy too. Isn't there a community dedicated to that issue?
• Ditto for the 'hateful content' (and I would add the extremely low effort posts too), it was a pain on Reddit, it's a pain on Lemmy too there is just of it on Lemmy because there are less of us posting ;)
  I consider the Reddit default home page an insult to any half-working brain but I would not be much more sympathetic to Lemmy's default feed either. I remember we briefly discussed that already: I'd rather see an empty feed by default, with only a short-ish selection of very broad categories the user would pick from to start seeing content that they're interested in. And only that content, not all the crap. They would then be able to start fine tuning their selection. Something like that.
• Reducing Reddit to what you listed here would be... unfair to the great content and great discussion one can easily find over there. As an ex-Reddit user, after an adaptation time (learning how to get rid of the default crap feed and how to remove the crap ads, learning what subs were better ignored) I had a great time using Reddit (and that is despite its poor UI). I did not quit using it because of the flow of hate or the flow of moronic content, nor because of abusive mods (quite the opposite, I appreciated their work... thx to fine selection of the few subs I was subscribed to). I did not quit reddit for that, no more than I would quit Lemmy for those flaws either. I left because I hated how Reddit, the corporation, took hold of our content and started restricting access to our content in order to negotiate deals with partners. And started talking about paywalling some of it. I briefly explained it as a last post on my Reddit profile and I close the door behind me. But I do miss those interesting discussions I had, and I miss a few subs too (r/Simpleliving, would be the first one I would mention).
  If I was not admitting I miss that I would be a liar.
• I also find it difficult to motivate/encourage more people to join and participate here on Lemmy because I'm myself constantly faced with the 'messy' aspects of Lemmy. I'm stubborn and I decided I could live with them (happily) but I also know many people are not ok with that and it's unlikely they ever will.

Hence me agreeing with the OP: Lemmy being as fragmented as it is is a critical issue.
Hence, the second part of my comment: it feels to me that the only easy/obvious solution is to rely on a centralized system. I'm not saying it's what should be done (I would not be part of the fediverse if I had no desire to see an alternative to that centralization). I may be wrong in that, most probably I'm (I have no technical expertise) but it still is what I felt while reading the post. Nothing more.

And for the rest, let the downvoters enjoy their very own moment of power ;)

Well, merging communities means trying to reduce the number of alternative communities on the same topic, or did I miss something?

But, like I said, I'm not saying it is not doable. I'm only sharing how I felt reading the OP post.

That's more like Proposal 2, and doesn't actually solve the main issues with duplicate communities. Proposal 3 solves them quite elegantly.

......get.......out.