

You might be thinking of PKI and certificate trusts.
Tier 1 in DNS terms are high-level peered (peered with other tier 1 servers in major network segments) and just refer requests either downstream or to other tier 1 servers. This is no longer as necessary with CDNs everywhere, and DNS infrastructure no longer has to mirror routing landscapes, but it seems that opennic.org is still organised in this way.
Anecdotally, I switched a small network to use opennic in 2019 and it was a disaster, never again. I see that the DE servers are still being recommended to me in Canada, so I guess nothing has changed. Opennic is an example of a good idea with terrible execution.

If the caldav and cardav specs were more practical and less insane, we would probably have a lot more choice in software to these ends.