Centralized servers aren’t archaic, they’re a natural outcome of how social systems work: finding communities is hard; people want to contribute their ideas, not play sysadmin; spammers and AI researchers will create enormous costs for you; etc. If you federate, you will have more time dealing with those issues than a single focused competitor and you are unlikely to see free contributions which outweigh those costs.
Everything you mentioned is available now on Mastodon, and it’s really interesting to see how that works. Some people love having a small network of their friends, but a lot of people have trouble finding people they want to follow. Instances can have their own rules but dealing with abuse is now a multiparty process and since a lot of instances are run by volunteers that can be slow, unreliable, and inconsistent. Some small servers get hammered by storage and bandwidth demand but there’s no great path to monetization unless you have a ton of users willing to pay more than most people are used to paying for internet services.
In general, these are social problems and there is only so much technology can do to improve them.