The self-hosting machines are plenty to avoid the problem you described, where there's massive slowdowns getting anything at all, including tiny little text comments. I hope you don't need me to walk through every detail of how a distributed system can do comments in a reasonable way?

But self-hosting machines are susceptible to the "I can only upload pictures and videos at 5-10mbps" problem. That requires more difficult peer-to-peer systems.

The first problem only requires getting small bits of data onto the same machine. The second problem requires getting large amounts of data onto many machines. Or reasonably symmetrical upload speeds.