Easy to say that but the reality is it would have been too difficult. You simply can't have 5 top class strikers on the same team, and getting rid of one or even two of the ones we already had last summer was going to be extremely hard. Balotelli clearly wasn't going anywhere and even if he did, you can't replace your 4th choice striker with arguably one of the Top 3 strikers in Europe. Same with Dzeko, who had only been bought a year and a half before, on a huge transfer fee, and who's on big wages. Tevez, too, couldn't move anywhere because his wage demands were so high even P$G wouldn't pay them.
At the end of the day, I'd take our striking quartet over United's anyday. People should be happy we have one of the best strikeforces in Europe and not cry every time we don't buy every world class player that comes on the market regardless of necessity.