This is the usual fantasy. But first, full disclosure: I've been using Proton for several years mainly because of its privacy policies and it's being out of reach of US Civil law where it's a free-for-all and money inevitably wins.

As for blockchain, pretty much nonsense. At least it doesn't have to scale that much for a smallish operation like Proton. As for security... well, nonsense. This is a private company that uses public infrastructure. That means there are more than enough openings for folks to do what they want with your information.

Fine, use Proton. But not because they have anything do to with blockchains. Rather the policies and legal framework.