Of the top of my head? Pretty much take your pick from any post made by Undertone or Quest that quotes someone siding with Mercy mains, and there is slews of it from many different people in Titanium’s new Mega Thread or the actual Mega thread at many various points before it turned into a clown fiesta of how quickly can it get locked.
Titanium’s thread: Why I Have Yet to Not Despise Mercy's Current State