If I had to pick, I’d say the game should be balanced around Diamond.
But I was trying to explain how overall stats can skew heavily towards ranks with higher populations.
Competitive Mode Tier Distribution
I also think, considering how Mercy went from being considered as throw pick in February 2018, to being considered a must-pick in June 2018, that it would be best to at least wait a month before making any judgments about Mercy.
Especially for the top 15% of players, where pros haven’t seen even one day on this current healer patch.
And the top 15% tends to copy whatever the pros do.