You didn't give much thought to this, did you?
If you increase m+ rewards, you invalidate heroic raiding as a whole.... The ilvl has to be lower than heroic drops... Or why even bother raiding when you can spam farmable content and be done in a week? And mythic gear has to be above heroic ilvl and the vault needs to rewards the highest ilvl the game has to offer, i.e mythic gear.
You could limit m+ dungeons to once a week but that would remove half the point of the content itself, which is pushing keys. And what would you do about leavers ruining a whole week?
The current system is better than bfa. That's a fact.