Then why change the players if it worked so well?
We beat a Chelsea 433 with a back 3, but Chelsea didn't play a 433 today did they? They played a back 3 too. Ole just got out thought, and everybody from the commentary i was watching to the matchday thread saw it coming.
The best thing about arguing your point is that you have the result in hand and can make any argument to support your claim. "Should have" doesn't mean anything, you can't know a thing about what would have happened. But we can of course say that: Today didn't work. For all we know your way of doing it could have meant we won 5-0. Or lost 6-0. It's just "what if" theory.
I prefer statistics.
What are the odds of beating Chelsea 4 times per season? It has never happened in club history. Are we faulting the manager for something that no manager before him has accomplished?
David De Gea allows 2 goals that he must save. Are we blaming Ole for not playing Romero for this game? De Gea has come from a series of very solid games. Romero was the cup keeper. Should he have started?
This is what we know:
The FA cup is a trophy but meaningless in the grand scheme of this season. If there was any game to adjust and rest players, it was today. He opted for a middle ground that didn't work out. The players on the pitch did not perform well enough. They have in the past, what changed? Are we ignoring that there is a team of 11 players opposing us that is also very good at football?
Is Ole blameless? Well no, we lost so he's not blameless. How much of the blame does De Gea take? Maguire? Williams? All cost the team goals today through enormous personal mistakes.
Is Ole to blame for playing Williams, De Gea and Maguire? Sure, who should he have played in their stead? Romero, <Literally no one> and Timothy Fosu-Mensah? Pretty easy to make that argument now that we know what happened in trhis game.
Did the players on the pitch perform as they should have? If no, who'se fault is that, Ole or the players who were given a job?