From the Github comment you are referencing, dannyperson states, "When NTP Pool warns that pool.ntp.org should not be a default, this warning is directed to vendors, not open source projects." but the clause from http://www.pool.ntp.org/en/vendors.html IS talking about Open Source Projects. The heading is "Open source projects".
What is the difference between a default setup and a default configuration?
That person on github is misunderstanding both Poettering and the ntp.org's policy.
MatejLach's elaborated on Poettering's point of view for that matter. https://github.com/systemd/systemd/issues/437#issuecomment-1...
* NTP Pool welcomes open source projects to use their servers
* They want vendors to register a vendor prefix
so there are two options, either systemd is a vendor, and can register and use systemd.pool.ntp.org, or it isn't, and can use pool.ntp.org
They could (register a "vendor zone") and use "[0-3].systemd.pool.ntp.org". They can, technically, even use "[0-3].pool.ntp.org", but the NTP Pool Project is saying they cannot use [the specific hostname] "pool.ntp.org".
That last part is what people are apparently not understanding.
Also, OpenBSD blatantly ignores it and uses "pool.ntp.org" anyways.