Platforms actually have one significant advantage over personal websites, blogs, disconnected forums: You only have to go to one website (open one app) in order to read everything you find interesting. You don't have to remember to go to 5 different forums and read 15 different blogs.
Of course the disadvantage is that they are a lot easier to censor because they're a single point of failure.
ActivityPub should in theory be the best of both worlds, but I am not too optimistic; people, organizations, governments wanting to censor people they don't like will always find a way. :(