So I played a game of Hexakill and went 0/2/29 as thresh. I got an A-. Riot it's time to stop putting so much of your score based on how much cs you get because a support who for every death had 14.5 assists should get better than an A-.
You're graded relative to others on the same champ in the same role, so you're probably not hurting grade wise because of lack of cs, since most thresh supports won't get many cs beyond that from relic shield.
(Also, I wouldn't worry too much about your grades in RGMs anyway, since you can't get mastery tokens there, and the S rank chests are limited to one per champ per season so you've got plenty of time to get that if you haven't already.)
There updating support grades in the next patch 6.14
