If you ask me, most of it was other support mains who, instead of asking for buffs, wanted Mercy knocked down a peg. I am not entirely sure it was “the entire community.” Sure, I saw a few DPS mains who believed she did not have counters (wut) and tank mains talking about how bloated her kit was (the irony). But those are rare instances. The VAST majority where always like, “why is Mercy must pick” or “why does Ana have to aim and get less value than Mercy” or “Moira is worthless because she does not have the utility that Mercy has.” I read A LOT of those threads and I was not seeing an entire community come together for anything more than a nerf, in the general sense, because they were obsessed with her pick-rate. The healing nerf specifically clearly stemmed from the support community, however.
That is just addressing the first sentence. After that, you ironically do the same with a weird passive aggressive jab at Mercy mains and call them all whiners which is somewhat fair. Albeit, I feel as though any group would “whine” under those conditions. In my opinion, Mercy was never overpowered but now she is balanced. By that, I mean, she did more than the other supports; however, that was because the other supports were quite weak. To that end, it was so much easier to just give Mercy a massive nerf and slight buffs to the few struggling supports to get the support diversity back. But I have a feeling we will encounter similar problems in the future because this is a bandaid solution.