Is this an online mode? I play career and tournament. I'm on semi-pro difficulty right now and can usually win 5-1 or 6-1 so I am about to change the difficulty.
In amateur, it's as simple as running straight to the other side and shooting. There is absolutely no defense. And to get the ball back, all you would have to do is run up to the defender.
Semi Pro is not too different, except that the AI spontaneously decides to play defense on some occasions when you are sprinting down their side of the field.
Professional is the first game mode where the scores won't likely being 6-0, 5-0, 7-1, etc. but it's still easy enough for someone to get consistent 3-0, 2-0, or 3-1 wins.
World Class is where it gets a little tricky. The AI is actually a threat to win a game. For me personally, I will win more than 70% of matches I have on world class, but that 30% tieing or losing keeps me honest, making it my most used difficulty.
Legendary can be very difficult for people new to the game. Although, it is very beatable for experienced players who know how to approach the game the right way. It becomes very difficult for through/over the top balls to be effective at this point. The AI defense is still much to discipline.
Ultimate team is clearly the most challenging game mode. It's winnable, like any other game mode, but the only way to win is through strategy or having overwhelming talent on your side. It becomes almost impossible to steal the ball from the AI. It's as if every player on the other team can dribble the ball like Neymar and pass like iniesta.