Pingbacks are back, baby! What is old is new again, except this time is centralized, so hopefully with less spam but also less independence once FAANG acquire the service.
Indeed! To be clear: webmentions themselves aren't centralized (and neither are the other various IndieWeb protocols), but webmention.io does provide a very convenient (central) service for receiving them.
Human nature finds a way to subvert some of the best intentioned technologies.
This is fact. We need to get used to it and solve the tough problems: identity, moderation, spam, discussion quality, community norms, and so on.
Building a service is often easy. Marketing it is harder. Building something useful to a group of people in spite of human nature is probably the hardest.