Torrents work for content that is heavily seeded, but you also have a lot of content that has ~0-5 seeders with very bad bandwidth.
I don't see how IPFS tackles the problems of guaranteed availability and enough redundancy while relying on volunteers to mirror and serve content.
Also, if you want to DDoS content, it sounds like all you need to do is find the IPs of the nodes that host the content you want to target (which might not be many, and I guess become visible to you once you access/download that content) and knock them out
Unless I missed something?