This would only make sense under the assumption that the DNS response can be trusted. For the vast majority of domains and resolvers, that would not be the case

This would only make sense under the assumption that the DNS response can be trusted. For the vast majority of domains and resolvers, that would not be the case. (I'm skipping the discussion of whether you'd want to trust DNSSEC at all.) The idea you're describing has been standardized as DANE, which has failed to gain any adoption. It would not make sense for CAA to try to do the same thing. Instead, it set out to provide a defense-in-depth mechanism for certain CA vulnerabilities that fall short of a full compromise.