We can all agree Mercy is overpowered in some way (except for the Mercy Defense Squad).
I don’t think the real issue is her resurrect, or her boost, or her combat healing.
I think it is her ridiculous mobility. Guardian Angel moves too fast, Mercy is rarely punished for continuously being out of position because of it. It allows her to get in and out of choke points and scraps with a consistency no other support can even dare to match.
Moira is toast after Fade is set on its long cooldown. Lucio is an easy target because his path is usually predictable and unless he sacrifices healing, he doesn’t even move that fast. Even with Amp It Up and the speed boost, he moves slower than Guardian Angel. We all know Ana and Zen have zero mobility.
Reduce the speed of Guardian Angel (current 20 m/s) to at least 15 (to be roughly in line with an amped up Lucio) or give it a REAL cooldown because 1.5 seconds is virtually non-existent.