- As pointed out in the previous comment, with DNS based blocking users often have to choose between convenience and privacy.
As an example: Blocking ads on Youtube with DNS blocking is very hard, unless you block youtube* itself.
- It does not give you fine grained permission: Like, if you only want to allow a particular third-party on a specific site.
While DNS based blocking is fast but at the same time it is also difficult for an average user to surf the web anonymously using the same.