This wasn't a description of Protonmail - I don't have much experience with them specifically and they may do some things differently, but of one's casual email service, like how people use PGP with existing mail systems.
I also do not claim that description to be 100% accurate - it's been a while since I've used PGP with email in practice, so I might misremember something. But to best of my awareness, this is how things are done today.
In my opinion, the main three problems with PGP today are: 1) lack of good no-frills "just works"-type tools; 2) issue with email metadata (at the very least, to/from addresses) being impossible to encrypt by design; and 3) abundance of haters (and they have a lot of right arguments, although many just boil down to the tooling issue and how it's easy to shoot everyone's legs with the current tools) who claim PGP should be buried (all together with email) - which is not exactly wrong.
I also do not claim that description to be 100% accurate - it's been a while since I've used PGP with email in practice, so I might misremember something. But to best of my awareness, this is how things are done today.
In my opinion, the main three problems with PGP today are: 1) lack of good no-frills "just works"-type tools; 2) issue with email metadata (at the very least, to/from addresses) being impossible to encrypt by design; and 3) abundance of haters (and they have a lot of right arguments, although many just boil down to the tooling issue and how it's easy to shoot everyone's legs with the current tools) who claim PGP should be buried (all together with email) - which is not exactly wrong.