They block by IP.
Changing DNS servers doesn't make any difference.
The IP address changing because of load balancing? How would that be an issue.
The ISP blocks the IP of the site. If said site changes IP by the time DNS filters through the new IP is blocked.
On the fly IP changing, or redirecting to another IP, won't work. The original IP is blocked, i can't t connect to it to be redirected.
A VPN gets round these blocks.
What happens where a web content publisher behind some website publishes the content on multiple servers at various addresses using a CDN or a DDOS protection service such as Cloudflare ? It then becomes much harder to say what ‘the IP address of the server’ is. If an ISP censors DNS in such a case then the user just avoids the evil DNS server.
As above. The IP i resolve from DNS for a banned site is blocked, I can't connect to it, how can i connect to be redirected to another IP?