One of my favorite fighters of all time, Roy Nelson was an absolute menace on his feet and had a killer overhand left that KO'd many people. Then some Eastern European exposed that he was a one-trick pony in a match where all the guy did was circle away from Roy's left hand the entire fight. Roy got embarrassed in that fight and he was never the same afterwards because everyone knew his Achilles heel. He was cut from the promotion soon after and then tried his hand at Bellator, where the competition also had him figured out. I don't think he fights at all anymore.
Yes, you have to be very well-rounded in this game because if you are a fantastic striker your opponent should know this, and work around it.