What I like about this is: It solves deranking problem. Everyone will aim for their highest rank possible to maximize rewards.
What I don't like about this: Everyone is rewarded the same for achieving particular rank. For example, I can reach mythic in X games, and someone else in 3X games, we both get same rewards. We lose competitive side of current reward system with your suggestion.
Also, maybe I misunderstood, but after mmr reset, I go to bottom of group 4, I can only get rewards from ranking up? Do players starting bottom of group 1 have more rewards available for them? This would cause everyone to reach mythic, then derank all the way down to group 1 before mmr reset to maximize rewards.