The major point of Protonmail, I think, is the no-access encrypted storage, not E2E-encrypted transit, which it does have, but only in limited and, as you point

The major point of Protonmail, I think, is the no-access encrypted storage, not E2E-encrypted transit, which it does have, but only in limited and, as you point out, problematic circumstances. If your concern is with state-level actors with the ability to do mass spying on emails in transit and collection from many different providers, then no, Protonmail won't be that useful. If your concern is with someone getting access to your email archive, possibly years after the emails have been sent, then Protonmail does offer something: even if its own data storage is compromised, your emails should be secure. I suspect the latter is actually a much more common problem than the former, as we've seen with data ransoming lately. Unfortunately, Protonmail's implementation is rather clunky. I actually would consider using a self-hosted system that did something similar: get clear-text emails, but immediately encrypt them with a key that the server doesn't have the private key for, and still allow searching and notifications in some way.