Season rewards based on?

So, with a few days left i went on the crunch time to reach the dream diamond(different account). Last night till midnight being the final stretch, I reached P1 promos 2 win 1 lose, then the season ended :|. Anyways, basically wondering if ranked rewards are based off MMR or division. Asking this because I was 100% sure it was based off division and like there are a couple people yelling at people who think it should be based off MMR. But i remember last season, where this account decayed into bronze, yet got silver rewards? Any insight?