Earlier quoted context omitted.
The only thing that bugs me with Proton is that it's still very complicated to integrate with thunderbird (or any mail app?), which makes it practically unusable for my needs. Having a tab always open in my browser for my mail seems so wrong.
Genuine question, how is a browser tab different than thunderbird? Besides storing a local copy of mail (which is obviously a huge win), I don't see a big difference. If anything I like the web UI better. However, for my uses I simply installed proton bridge + apple mail. It just works with all email services I use.
Different protocols for one thing - HTTP vs IMAP and/or POP/SMTP.
Each webmail app does things it’s own way. Webmail conflates the app and the protocol and the provider. Some people prefer to have mail from different providers in a unified app.