I think something is needed between Mail Plus and Unlimited. Proton offers to many features that I don't use for example while I still love the core concept.

I would love Mail Plus but need 3 custom domains. But nothing else that Unlimited offers. The constant upselling and adds brought me to Unlimited 2 years ago but i cannot excuse the price for me. I simply don't use anything else then Mail. I also think that the constant upselling really overshadows the core idea of privacy as I feel more and more pushed towards buying stuff I didn't create an account for in the first place.

TLDR:

Adjust Mail plus or make optional addons for small fee i.e. extra domain 50cents extra or so.