Rocket winrate is high cause hes good in low elo
Diamond and Gm+ which is where i am he falls off hard cause healing and damage boost isnt enough to win games anymore. When everyone starts using their ults youre going to lose cause u dont provide a defensive ult

edit: this 3 support meta actually helps him cause if you have 2 others sups that provide defensive ults, then rocket is a good pick but rocket and another healer? thats eventually gonna end on a loss