Every character has at least one bad match up (4/6 or worse) in my opinion. Some characters can overcome even their worst match up. However if you are doing whatever it takes to win, then having a team of characters is your best possible action. Even the best characters (imo - Sonya, Smoke, and Kabal) have match ups that while not devastating, are worth re-picking. Sonya can handle Kenshi, but why use her when there are easier options like Kung Lao? Smoke can beat Kung Lao, but Cage can expose him. Kabal can overcome Sektor and Jax, but Smoke/Cage can do it with ease.