Well I doubt the backlash against the game is soley directed at the twist and not just the overall lack/bad story, repetitive mission design, structure, open world use, and lack of MGS Personality.
But yeah that retcon is possibly one of the worst retcons in that it was really unnecessary and fucks up things just as much as it supposedly makes sense of things, these things being thigns that did'nt need to be made sense of.
Even if it explains why in MG1 Big Boss sent Snake to kill well Big Boss. It can already be rationalized as well Big Boss never expected him to succeed anyway and him fighting Snake is his plan gone awry. Also MG1 especially exists in canon only as a reference point. It's connection with the overall MGS series really doesn't fit and MGS can easily pick and chose whatever it wants. It's best to think of the events of MG1 and even 2 only in how the MGS games chose to use them. MG2 is a little bit better as it really does closer fit the MGS series.
I guess it explains how Big Boss survives, but again MG1 doesn't say he died and well this did'nt need an explanation anyway. It's MG, dude just did'nt die. He apparently did'nt even die in MG2 so who cares. None of this needs an explanation.
It's a strange retcon, because I'm not sure what it's actually supposed to do.