I have been a longtime user of Superhuman but since they increased the price and now have been acquired by Grammarly (see discussion: https://news.ycombinator.com/item?id=44433994) I want to find an alternative.

It doesn't need to have all the "AI" that Superhuman has but keyboard shortcuts and hotkeys are a must. Must also have a mobile app

I've tried Spark, Shortwave, Apple Mail, Gmail, Thunderbird and none of them really compare.