Blocking DHT bootstrap nodes only takes care of DHT. This is only one way of obtaining peers, so even if it's not available, you can still fetch peer information from torrent trackers and receive potential peer addresses from other nodes through Peer Exchange.

DHT is required when your torrent file does not contain any tracker URLs (and you didn't add any yourself). In this case if it's blocked, then you have a problem.

Private trackers typically disable DHT for all torrents (so their torrents don't leak to outside users), along with PEX. It's just a flag in the torrent file, so you can force-enable it if you want (but it won't help much since the vast majority of other peers will probably abide by the rules).

Those are used only by new users the first time they use the app. They are regularly blocked, or retired (because maintainer decided so), it does not affect the network because they have nothing special. New ips are added to the list. You could become one of those simply by letting your computer online 24/7.