As for the original question of the thread, i think any US team as they are currently would struggle in the premiership. However this doesn't mean they would be relegated for sure. They would fight to avoid relegation, and in a good season get a midtable place. Fighting for better (a place in Europe) would be nearly impossible at first.
As for the World Club Championship, it's not that they don't take it seriously but most big teams in Europe have huge schedules (even if not as big as in Brazil) and are also playing in European competitions where they actually get a lot of money from. They would always pick a Champions League win, or even a UEFA cup win over the WCC. On the experimental WCC the final was between Corinthians and Vasco da Gama (two brazilian clubs) who were by far the best 2 during the tournament. If it was to become an important competition in which every team would field their best eleven and try to win it, the major favourites would always be the south american and European teams. However the current format of Group Stages/Knockout Stages, gives a better chance to the other continents teams as they would probably give all they can and more to win it, and as there were only 5 games for the finalists in it, they could have more of a chance. Afterall in this format, a couple bad games and you're out. It could happen to any team, good or bad.
Finally, as for Essien, i think you're reading too much into it. It's perfectly natural that it's his dream to play for Manchester United...AND Chelsea... AND Arsenal. It's not because he walks around with his Manchester United Kit on the streets because he supports them and has supported them his whole life, it's his dream because it's his dream to play in a top european club. He'll obviously want to go to a top team, and when selecting one, if given the choice, he will obviously pick the team who will provide him the best conditions (read... money).