There’s also currently too many steps for users beyond “install app, turn off brain, and start scrolling”. As sad as it is, that’s all many people want: an app that lets them mindlessly scroll.

I agree with your overall post, but I think this part is an especially major limiting factor--the selling points of a decentralized system are also disadvantages for mass appeal for a lot of general users. Most people just want something they can open and have everything already set to go and with everything in one place. And honestly I see the appeal of that. It comes with its own disadvantages, but sheer ease of use is hard to beat, and decentralized systems that have a higher barrier of entry to access content have a leg behind on competing with an immediate one stop shop. I think the overall competition is going to be in quality of community rather than population capture. I don't see decentralized systems outcompeting in the latter category.