Your analysis is decent but has to much rage and emotion in it as I see some drastic stuff that you said here.
I do agree that this lineup was questionable. The fact that Park played after not playing much throughout the season and being rusty didn't make much sense. We started off well when we pressed them and kept a high line. Then once counterattack from Man. City and we are put into our shells. Park doesn't go forward anymore, so that leaves the forwards Rooney, Nani, and Giggs isolated as they get no midfield support. As a result, we are pegged back in the first half. In the second half, we go to a 4-4-1-1 and bring in Welbeck and get better, but Rooney gets off form and makes many mistakes, whilst the right wing does not provide much good supply with Jones' crossing ability not that good, which is understandable. Our wide and forward players couldn't get much support with Rooney often struggling and Nani lacking support, thereby getting himself isolated. With our four attacking players having a tough time breaking down Man. City as a result of two not at their best, we needed someone else to provide a spark and get things going for us, another attacking player when Man. City were getting defensive in the last 30 minutes. We needed someone like Cleverley to come in and really give us a push. However, we couldn't do so, and we struggled to get a shot on target.
The initial approach really did it for us. We couldn't release ourselves from the defensive shackles, and so we had a tough time on the final third.
Rooney is never a player who can play up front on his own, no matter if he did play there during the 2009/10 season. He's not that kind of a player, naturally. And if a player is rusty and hasn't played in a while, he shouldn't be risked in a big match. Then again, that risk worked with Smalling, so that isn't the case, then.
I guess the main thing was that we shouldn't have taken a defensive approach. In the FA Cup, we weren't defensive from the off. We attacked them, pegged them back, and got 3 goals as a result. They went defensive, then, and we saw off the game, albeit by conceding 2 bad goals.
Now for the positives. Our central midfielders Scholes and Carrick and our defenders were immense. They contained Man. City's flair players and shut them down, therefore leaving them with only 5 shots on target. Smalling was excellent in his return, and Jones looked back to his best. Ferdinand and Evra were good at filling in the gaps, even when Evra was often in a 2 vs. 1 with Giggs staying up front. Speaking of Giggs, he was also much better and looked more at home out wide where he doesn't have as much responsibility as he does in the centre of midfield. He was creating chances, but there was rarely anyone to finish them. He couldn't link up with many people as Rooney was off colour and Welbeck was closed down by 2 defenders. He could have had a greater influence had we not have had such a defensive approach.
I guess what I have to say here, to finish this off, is what's done is done. Move on, and look forward to the next match. Whatever has happened here has happened, and we can't do anything about it.