Yes, that's absolutely true. Assuming a full PGP flow, (e.g., proton to proton) even in that case the recipient and other metadata (in tuta, excluding subject line) is still visible to the provider.
Hopefully the more people move to secure providers, the more the general case will be transparent PGP, but we are a long way from there...
This comment is a perfect example of why I have written https://loudwhisper.me/blog/proton-fediverse-burnout/
The 88 thing is the complete tip of the iceberg for me. I can't honestly imagine the thought process needed to reach a conclusion that a Taiwanese guy (8 is a lucky number) born in '88 would put that number as a dog-whistle (which is not really part of his own cultural landscape) for Nazis, while dealing with a PR issue.
It's like looking at a crashed car, tire marks on the ground and suggesting it must have been a sharknado and not a car accident.