That's not true, at least for VirginMedia. I use Cloudflare DNS servers and I can't access ThePirateBay without a proxy or a VPN, it's more than just a blockage at the DNS level.
When I was on virgin, I noticed that ip addresses used by some TPB or similar websites weren't routed to the internet, which is obviously quite bad. I'm not sure if it's still what they do.
Better ISPs only do DNS blocking though. Some don't block anything actually.
Until encrypted SNI/encrypted client hello is a thing, the hostname is still sent in the clear.
Also, it can still be DNS blocked - just because you use Cloudflare's DNS doesn't mean they can't rewrite the responses as they still transit unencrypted. You'd have to use DNS-over-HTTPS or DNS-over-TLS to work around that.