That statement is made as if it is fact. That is an opinion. I personally do not find Mercy to be fun, and her impact is relegated to her main cooldown ability that contradicts the inital desire from the developers to not encourage Mercy to stop healing for a time and hide addressed in her rework.
I’ve said many times she requires no changes, but the developers change heroes even when they do not.
I talked about this extensively in a post I made here, if you’re interested.