This point has been acknowledged since day one though, and it is not a point specific to ProtonMail. Any E2EE service that has a webapp is susceptible to this, and that's essentially all E2EE services out there.

The only way to address this point, with current technology and current standards, is to discontinue the webapp and force everybody to the native apps on desktop and mobile. It is the opinion of almost everybody in the industry that webapps are necessary, and that's why we, WhatsApp, etc, all provide webapps.

So the point is acknowledged (and has always been acknowledged), but the opinion being expressed (remove the webapp) is not something that we agree with.