Twitter's format feels a bit like yelling into the void and waiting for replies...you may luck out and get some engagement from a hub or a small subgraph of the network. Mastodon makes that stronger by removing the algorithm (I'd like there to be a user-customizable feed sort algo by an array of parameters, not sure what the technical limitations to that are: processing, security?)
Comment trees feel better (to me at least), because there is a hierarchical origin, a native indexing by topic>post>comment>countercomment...it sort of resembles how we relate with the world or navigate maps.
they don't need to, they just need to seize the ground PoPs and block ips to make it unusably slow.