At the end of the day, I am the one person who has to answer that question/is responsible for being GDPR compliant. I've spent hours doing research, figuring out what we need to do and implementing it -- and it's a hollow victory because even though I've said yes and have 100s of articles/white papers/opinions that back up the decisions I've made, the real answer is still "I don't know".
And I absolutely know I'm not alone in this. I got GDPR compliance dropped on my lap because I did security compliance -- if you contrast NIST 800-53/800-171 against GDPR you'll see why people are pissed off. One has clear guidelines with enough room for evolving best practices written by obviously competent/experienced professionals, the other is written as basically "we'll know it when we see it".
Sounds like a win for the GDPR to me, we know rigid checkbox-ticking is ineffective.
Apart from that, NIST 800-53/800-171 are catalogs of "security controls and associated assessment procedures" for "Federal Information Systems and Organizations". GDPR is a data protection regulation in the context of the EU legal system. Apples to oranges.
What if my opinion of what is ethical differs from what regulators decide? Opinions are notoriously inconsistent, subject to bias, and easily used to discriminate.