The left behind meme is Capcom's PR guy saying "haters will be left behind" as a response to all the criticism the game has rightfully received. Their PR guy is pretty much the Derek Smart of PR, he does a great job of just angering the playerbase more and more.
So it's a way of folks venting anger at Capcom- SF5 hate is a bit of a meme in itself, though there is plenty of reason to crap on the game. It's the Elemental War of Magic of fighting games in terms of the mistakes, and they really haven't improved the fundamental problems enough yet (that said, the input delay problem is an engine problem and might not be improvable, Tekken has similar issues, though it's not as bad in Tekken due to Tekken always having higher input delay due to its nature as a 3d game)
The sad thing is that looking at the upcoming MvCI, it really looks like Capcom has learned nothing and forgotten nothing, the exact opposite of Stardock's response.