I'll give a different point of view.
I switched my personal email from Google Workspace to Proton. My use case wasn't privacy (especially when 99% of my email is sent to and received from people using Gmail, Office 365, etc.) I was interested in trying Proton more to support a plurality of service providers.
As such, I'm probably not Proton's target customer. That means the compromises Proton makes to enable E2E are not worth it to me.
Some examples:
* Search is like going back 20 years.
* The lack of automatic filtering (e.g. Gmail's automatically applied Promotions, Updates, etc labels) has made the signal to noise ratio in my personal inbox so low that I'm considering just taking the app off my phone or suppressing notifications, at least. I don't have the time to set up manual filters for everything that comes in.
* The lack of automatic filtering and decent search means that my personal email is now pretty much useless.
Similarly, it's pretty hard to migrate away from because you can't just use IMAP to shift your email history to another provider.
This isn't a negative review of Proton. This is just to say that choosing Proton Mail means living with the compromises necessary to enable their main feature (privacy) and I don't care enough about that one feature to make those compromises worthwhile (because my email is going through so many non-private services anyway).