Not sure if this was posted here… but here are the stats as of Day One of Season 9 until Monday March 5th 2018.
So Overbuff isn’t that far off on the weekly basis at the moment but you have to bare in mind the Weekly is passed off the last 7 days and not from day 1 of Competitive and Monthly is last 30 days and not from day 1 of that seasons competitive…
But Mercy is largely put in place so there is a unlikelihood she will be altered.