The author merely suggests that those 29 or in someway trusted by a lot of people to handle DNS queries. Those 29 also publish information on what properties the service have. If you read the whole page, the author also lists other publi DNS resolvers worth a mention.

For the long tail of unknown open DNS resolvers, use Shodan. But I would not suggest that you use any findings from Shodan to trust your internet usage with.

Yes, SNI is a generic internet privacy problem. However, it is not a property of DNS. On the positive side, ECH has been pushed through the IETF and should slowly be available to the general user.

/ The author