It has a built-in option to point it to your extracted GDPR data, and will edit and/or delete all the comments that are listed in there.
Just configure it according to the instructions, and then let it run unattended for a while. It took about 15 hours to delete the 13000 comments on my 12 year old account.
You can't really blame this on the people. The centralized platforms offered something that for most people worked a lot better than what was already existing. In the beginning, those corporate platforms were actually quite good so it's only natural that people flocked to it.
It's only after those companies achieved a monopoly in their market, that they started pulling a bait-and-switch and began to enshittify their sites. Network effect makes it so that mass migration to something that's technically better is unlikely. This bait-and-switch is where they stole it from the people.