Barca press high as a collective unit so defend in a totally different way to utd. They also have Busquets, whose positioning is fantastic in terms of intercepting and closing down.
Bayern often play Lahm in front of the back four, as they did on Saturday, to act as an anchorman. If it's not Lahm it'll be Martinez or Schweinsteiger.
Besides, Bayern and Barca are both better defensively than United, so need less protection than those two teams. The Vidic-Ferdinand partnership is so vulnerable to pace and agility. Carrick doesn't provide the necessary help there.
You've described Carrick in two sentences.
"They also have Busquets, whose positioning is fantastic in terms of intercepting and closing down." - Carrick. Busquets isn't "fantastic at closing down" at all, but he makes crucial interceptions. They don't need a defensive minded midfielder because they keep the ball.
"Bayern often play Lahm in front of the back four, as they did on Saturday, to act as an anchorman. If it's not Lahm it'll be Martinez or Schweinsteiger" - Carrick. Are you blind? He does the exact same job. Schweinsteiger isn't a defensive minded midfielder.
United's defence is fine, maybe aside from Ferdinand. He can easily be replaced by Evans or Jones and our defence will still be fine. You're making excuses. You think Utd's issues are here because we don't have a midfielder like De Jong? You think a midfielder like that fixes everything? You think having two midfielders sit in front of the back four makes any kind of sense remotely? No. We do NOT need a midfielder like that.
So far we have had three big games of the season:
Liverpool away - We had the most possession and had complete control of that game. We couldn't create a single chance because of how poor our midfield are creatively. RVP was absolutely isolated and not in the game at all. We also had no Rooney, or anyone who could at least support him or be comfortable on the ball.
Chelsea home - Again, had great control over the game. Periods of utter domination in terms of possession as Carrick was left free to do as he pleases. But, once again, we couldn't create a single chance in the final third due to how poor we are creatively in midfield. Our wingers can't take a man on (Young needs to be sold on a free, Giggs shouldn't be in the squad, and Valencia can really only play well offensively with a Rafael behind him), so we have to play creatively through midfield. We didn't, and we drew 0-0.
Man City away - No control over the game because City pressed high. City have joined the list of teams that press high against us which consist of the likes of Barcelona, Bilbao, and Swansea which completely nullifies our possession game because only Carrick can keep the ball well in our midfield. If you close him down high, then you have control over United. But hey, losing control of possession isn't necessarily the end of the world, because if we still impose a threat going forward then we can counter attack like we did last year, and like Bayern did to Barcelona. Guess what... we have no creative midfielders or midfielders comfortable enough to pull a counter attack off. We countered and gave the ball away.
Our problems do NOT lie with midfielders who can't tackle, it lies with midfielders who can't keep the ball and be comfortable. United need to play with much more energy - pressing much better - and play much more creatively. We do it against the smaller teams, but we shut up shop against the bigger teams because we have the worst midfield in Europe out of any top European team.