What to expect:
- A premium task manager integration or at least the ability to access deep links (Newton, Airmail, Dispatch - Spark, albeit subpar)
- Rules and/or automatic filtering (Sanebox, Airmail)
- Send later (Newton, Spark - Airmail, albeit buggy)
- Snoozing (Newton, Spark, Airmail)
If you look closely, you will see the Venn diagram has no intersection.
If Mail meets your needs, great for you. But this is not the subject here. It’s about power features that became quite commonplace and yet cannot be all found executed flawlessly into a single app. 
I’d be willing to pay too for such a tool. Or, you know, just try to develop one. 
(an undertaking which is likely to drive me even more insane.)