It is also security theater. 99.9% of the time the other side you are communicating with stores their mails with server-side encryption. If your fancy encrypted e-mails have a "plaintext" mirror, your encryption is useless.
You want to optimize your 99.9% case for convenience (say, use Fastmail), and optimize your 00.1% case for security (manually managed PGP with a secondary anonymous e-mail). It makes no sense to trade away swathes of convenience and security just so you can be lazy with your 00.1% case.
I view Proton Mail as the convenient 99,9% case. It's a very polished service and it seems to offer a somewhat higher security baseline than the other email providers which probably don't even try to do anything encryption related.
The maximum security manual OpenPGP 0.1% case is still absolutely necessary though. No doubt about that. Anyone claiming that Proton Mail solved this doesn't actually understand how OpenPGP works. Not that I would fault them for failing to understand this ludicrously complicated stuff.
You want to optimize your 99.9% case for convenience (say, use Fastmail), and optimize your 00.1% case for security (manually managed PGP with a secondary anonymous e-mail). It makes no sense to trade away swathes of convenience and security just so you can be lazy with your 00.1% case.