It's not delusional, it's true. The only difference was, as you say, that it turned out that we weren't that good at playing it against decent teams. No-one is trying to say that we played like world-beaters, just that we tried to play the same style as world-beaters.
Wasn't there a statistic that under Gus we rarely, if ever won, after conceding first? If that doesn't show the limitations of only playing one way then I don't know what does.
To be fair to Jaap Stam, he's trying to introduce his style in a much tougher league than Poyet did in League One...