Well try and look at League like a sport. Some players have off years. If you are having trouble being successful with a champ I would suggest trying a different champ. For example I LOVE to play Shyvanna, but to do well I have to be more careful than people who would play say Riven. Now the balance may be off a little bit, but with soooo many champs, to have them all balanced is quite the chore, witch is also why patches come out so often.
Another thing I recommend is if you get to the point where u hate a champ, Play the champ. Now that may seem crazy but, there is no easier way to see the weaknesses of a champ than to be the champ. Now I understand where you are coming from but it sounds to me like you are in a slump. When I get like that I either take a small break from the game, and then try again next week, or I just try playing the game differently. For example sometimes I like to play Shyvanna top with smite, and then steal the enemies jg at the start of the game. Now I don't neceicerally recommend doing it but its fun to me.