You're right that I need to add more value. My planned direction is more along the lines of utility than security/privacy, which I think Protonmail covers pretty well. There's a lot of interesting value-add to be done in email.
The pricing is more that we offer honest pay-as-you-go pricing, with caps to make sure you don't actually get a ruinous charge, in direct contrast to "billing something reasonable for a whole year". If you'd rather do the former, then yeah! You're really well covered in the email space already. But I think people are getting subscription fatigue, where every service imaginable wants its $5/month cut of the pie.