Yeah the main problem is that the main reward people are going to want for mahjong by playing casually (the roll) is something that SHOULD be "Win 5 games" (assuming the ranking reduction ISN'T meant to happen), but realistically becomes "Win 5 games in a row" and if you ever dip below said ranking you're just going to reset it so you have another/easier chance at it, which as you said, just ruins everything.

Like if the titles are just meant to be a bragging rights thing, they could just remove the ranking reset, allow deduction of points at all times and make the roll achievement "Place 1st or 2nd in X games of mahjong (Ranked match)" while leaving the titles for people who really want to play/get good at mahjong.