Let's not forget that it was mostly a manual process for most of us. Someone would obtain a cert, and email it to you, along with the private key. I'm sure old JIRA tickets would have so many "encrypted" zip files containing RSA 2048 keys and leaf certificates valid from 2008 to 2011.

Such an excellently written articles with really nice interactive visualizations!

If a registrar requires you to use their own nameservers, then they are no longer comparable to other registries.