My problem with it is that it unwittingly reveals both of the reasons that the whole story fails for me.
A) The "Big Boss's legend is false, and Big Boss eventually lives up to it which may be the real turn" idea, by the post's own admission, has been done far more effectively in past Metal Gear games already. MGS3's ending where a devastated Snake receives the title in a sham of a political ceremony after learning everything was a lie, MGS4 having EVA outright talk about how his legend was exaggerated and Big Boss's final regrets, and PW's whole "I'm just Snake (60 hours later) Call me Big Boss... we all may be going straight to hell," they all work better than a flimsy last minute twist where Big Boss tells a guy "by the way you're a fake but you're also me because legends, I had to go do... something, later" and said guy goes from absurdly heroic to despotic apparently just from that
B) The fact that you have to spend so much time trying to figure out and reconcile the twist with the original game, Solid Snake discovering Big Boss has betrayed him and taking him down, the foundation of the whole series, and all of it is just conjecture.
When the MISSING LINK, FOR REAL final game in a series ends with a twist rendering it mostly a self-contained sidestory that answers pointless lore questions nobody asked while raising new ones that had no business being raised, defending it by accidentally pointing out that other games did these things way better and having to write fanfiction connecting it to a 28 year old 8-bit title just goes to show why it's disappointing.