I agree with 1.

I disagree with 2. Tuta works on multiple devices at the same time. Empirically

A. My point about having all data at rest encrypted still stands.

Depending on your threat model, having properties one, and a are sufficient. All of your historic data encrypted at rest has value for people.

I also agree with your statement about keeping all of your mail history local on an encrypted drive. That would also work. But you lose the cloud aspect of having a completely client-side encrypted service provider

Clearly tuta doesn’t fit your threat/usage model. But it does work and does provide a valuable service/trade off for people who want cloud based client side encryption for data at rest.