Even if it is an advertisement, can the threats be true?

I am not associated with any tested company or this blog.

I am an ordinary user of all Proton products since his birth and I love him.

Because the test looks credible, I just want an expert from Proton to dispel my doubts or honestly confirm the problem.

In that case, it seems to me that the only threat is the mindless copying of public keys to other servers, as described in the article. But who does so? Do admins not create separate private-public keys for each server?

Thank you for the explanation!