Why are people calling Mercy an off-healer?

[BadWidowEU-2419]

No hero should be have a winrate below 53% (or 52%. Not sure) in GM… That means most pro Mercy’s in GM can’t even consistently stay in GM.

This post explains it well:

A month of Mercy nerf in numbers

The support patch came out on August 9th, and no part of it has generated as much discussion as the Mercy nerf. I’ve seen a lot of claims since then about Mercy’s state in the game that need clearing up. In order to address these claims from an informed position, I’ve looked at one month’s worth of data from Overbuff. I separated the data into four weeks - August 9-15, 16-22, 23-29 and September 2-8 (Note: September 1 was the first day of season 12. Overbuff has no grandmaster Mercy data for th…