5x5 rounds give an unfair cardio advantage to the champion. Jon Jones is the supreme example. He has massive almost unmatched experience in 5 round fights while most of his challengers have little if any. He's been training non-stop for five round fights for a decade. Now take Dominic Reyes. For most of his career he had been training for 3 round fights. Jones was his first five round fight that actually went five rounds. Of course he gassed in the championship rounds. It was literally his first time! This discrepancy has really changed my outlook on champions (not just Jones). They have an unfair advantage especially if they have a long reign. They are training under different rules against a challenger who is often brand new to the rules. All fights need to be the same length of time. There aren't extra quarters in the Superbowl.