Well, I don't think so. Just to be sure, I'm talking specifically about gold rank. Most hit-scan players at that level just don't have the accuracy to deal with Pharmercy. Because of that Pharmercy at that level and below is insanely powerful. And again, I'm not saying that Mercy should completely ignore the rest of the team. She can move around as needed; I do that all the time. If I am not healing someone, then I am damage-boosting Phara. And damage boosted Phara is better than damage-boosted 76 or McCree, because she does more dmg per shot. Also, she is more mobile, she can get past all the chokes and shields and destroy the squishies first. Soldier or McCree can't really do that. Bastion, on the other hand, is another matter, entirely. I would almost always prioritize pocketing Bastion over Phara.
I don't think that's completely true. I, of course, don't have any hard evidence, but judging by how many people ask for 2/2/2 or for at least 2 healers and one shield tank or ask for a hit-scan hero or tell someone to switch off that widow/hanzo/[other non-meta hero], I dare say a lot of people are playing to win.