My key point was "unless there is a good reason not to". And in many cases there is a good reason not to use E2E encryption, like the example you have given. But in the case of Ntfy, E2E encryption would be a perfect fit, and eliminate any need for self-hosting.
I'll be blunt - as someone who worked in the space extensively... if you really need e2e encryption, you want to be self hosting anyways.
By the time you're trusting a hosting provider to properly do e2e for you... you've basically already lost the game. At any point they can update what's running and remove any/all protections you think you have.
So again - what is your threat model here? Because it sounds like you want "super convenient" and also "super secure" and those aren't two options you just check off - they're really more like diametrically opposed sides of the same slider.
