Would anyone be here, on steem before, hive now, if there were no rewards?
Yes.
How many?
Not many.
Decentralized! (well, less centralized data storage, more censorship resistant (not censorship proof))
That might be attractive to some, especially those being censored. But the place where there are people is where people go. Bitchute, Odysee instead of YT. Parler, flote, etc instead of FB.
Even with the ability to earn something, potentially, steem and hive are not as popular. Why?

The rewards are what attract people when it's not as popular as other sites.
So what's the problem with leofinance? There isn't one. It's a niche site. Anyone can create these niches, "tribes", and tokenize it.
Why did LEO go up in value faster than HIVE? Less people know about it and trade it? Making the market easily supported by the people who want it to succeed? That means they have more support from people within their community who believe in what is being built, than exploiters looking to just pump and dump coins like happens everywhere. People with money are into things about money. So LEO got lots of financial influx into their token. The founder is doing lots of dev, attracting investment into their platforms (leofinance, cubdefi)

A place where there is hardly any dev is not going to attract much influx into the platform via a token. LEO has what it has because it's been earned in large part. Hive/steem dev is slow, but the foundation by Dan put something forward that none had before: earning for posting content others value and reward you for (at least, that's the theory that applies to most, but not some like me).

I read your post, what is the negative feedback loop you say is needed here? Flagging? The negative feedback loop such as flagging doesn't do much to help when it's only applied to one person (or a select few). Maybe if everyone who was earning over $X each day was being flagged, maybe that would be "more fair", but still bullshit and doesn't fly in terms of allowing people to be successful by earning their way. "Sorry, you have reached the cap for success" or "you have a cap, but others don't" lol.

"Hey, invest in a token, where you can reward others who you want get rewarded and also earn curation rewards for doing so. Sounds good right? You get to reward content you like, make it successful, and you get to earn as well... that is unless those with more wealth don't agree with you, and they take away the rewards you gave the content, and then they also take away your curation rewards at the same time... while others get to cast their votes, reward what they want, the rewards stick, and their curation is kept intact. And then the ones who support downvoting (while also being the ones who aren't downvoted and get to have only the positive side of the system play out for them in their favor) say 'well you just have to buy more of the token so that you become more powerful in this plutocratic system', so just spend a few million dollars, no biggie!... so hmmm... maybe you shouldn't invest in that token since you could be shoving your money into a system where the rules you thought applied to everyone might not actually apply to you or those you want to support, because of what you chose to support, because those with money/influence can decide to not allow you to play by the same rules everyone else gets to play by (i.e. rewarding what you want to get rewarded, and having those rewards allowed to be kept there, and you making the curation rewards for making that choice to reward that content)"

And the you have people who are flagging as content-reward police, telling the person they are flagging that they should get their followers to buy HIVE and upvote their content. Right, go buy HIVE and have the content you want to support (maybe) get flagged where your support for that contents gets taken away and your curation rewards taken way. Great selling point! Maybe it's still better than straight donations for the one doing the donating? They get 'some' curation rewards by voting for others as well, so long as that content isn't flagged either?

I went over to try LEO because I'm tired of 4 years of flags. I thought, hey maybe if I don't post on things that the wealthy accounts don't want to see and flag (bernie, then curangel), maybe I won't get flagged. And I get to keep my rewards there for the most part if I do get flagged on hive. But anyways I get to keep rewards rather than have them taken away. Yet, I still get flagged because it's bernie leveraging their delegation to curangel to get downvotes applied, 95% sure of that as they delegated the same day curangel flags appeared again. Other people who post and get highly rewarded get to keep all or most of their rewards, but.... not I apparently (over 50-75% removed). They get to fully benefit from the system, while less so for me because the wealthy decide that's how it will be. So it doesn't matter what I post, the hate of the poster is what matters to those with the ability to flag them. And so it is, but "stop complaining about downvotes you!" "Go buy HIVE!" LOL.