Ken's cardio was not the problem in that fight. Three things hurt Ken.
1) Cutting the weight- Ken definitly is not as good of a wrestler as he thinks, he definitly did not cut weight well for this fight at all. He was so cut you can tell he definitly cut to many carbs out of his diet, He must have been worried about the weight because he came in 4 pounds under weight and sucked out. Perhaps tito's best advantage in this fight was knowing how to make the weight. Also he came in kinda wet looked like he was working out pretty hard in the back. That is a big mistake if you are already feeling sucked out, He should have been drinking and getting carbs in his body and just a light workout before coming out just enough to get the sweat going.
2) Overestimiting his wrestling. Tito owned every part of the fight that had to do with wrestling. He controlled every clinch got the takedown pretty much anytime he wanted. Ken was in control of the match with the striking in the first round until he tried to go to the underover with Tito, tito shrugged off Ken broke his base with a hip bump got the takedown and pretty much put Ken defensive mode for the rest of the fight. For some reason Ken kept trying to tie up with him (I am not talking about the Tai Clinch Primo, just Ken accepting the tie up without trying to punch out of it) the two times that Ken tried to get out with strikes, the first got Tito's attention, the second rocked him. SHoulda changed gameplans, but that is the one thing Ken never does, he tries to work his gameplan no matter how bad or good the results are.
3) If anything he overtrained for this fight. Look how beat Ken's face was before the fight started. They train to hard, When you are thirty eight you have to train smart as well as hard. I think Mo Smith is the best example of this. There is no one in his stable of fighters that can push Ken any harder or attack him with takedowns like Ortiz. If he was smart he would have trained with Hendo, coleman, Randleman someone like that. Ken should have worked more on his guard attacks. Ken still is not on the level with his guard. He should have known he was going to be on his back and worked the guard. That is how frank beat Tito.