Let's look in practice, as they exist: look at VAERS for example, it's in this exact situation (these are public records posted on a public and non-confidential HTTP server):
https://vaers.hhs.gov/data/datasets.html
This is the type of raw records we are talking about, and they carry useful information.
Yes, maybe the dates could be anonymised better, if I know the age of someone, and I know when he got his vaccine precisely, and when he got his MRI and why he did it, then maybe I can find and connect back the record.
But how likely this attack can be done in practice, and why would you do it to someone who already disclosed part of their records, plus how does it scale ?
However, the benefits are really present, it's not sharing just for the sake of sharing but to bring advance to the global research and knowledge of medicine.
In practice, who is it ?
I don't know, who can know ? Doctors who can tie it to other pieces of information that we don't have...
However, in the meantime, the researchers and doctors who don't have these foreign keys, they can totally do interesting and useful discoveries about drug interactions and vaccine side-effects.