Cardio is not athleticism. Anyone can develop cardiovascular endurance. That's why football/soccer is popular worldwide.
Israel Adesanya, Edson Barboza, Kevin Lee, Jon Jones, Mike Perry, John Dodson, Johnny Walker, Eryk Anders, Yair Rodriguez, Dan Hooker, Alex Oliveira
If you're "not talking about skillset, just athleticism," why does your list nearly exclusively consist of champions, former champions, and #1 contenders?Robert Whittaker, Volkanovski, Khabib, Reyes, Overeem, Garbrant, Usman, Costa (questionable cardio), Wonderboy, Luque?,Zhang, Joanna, Shev, Nunes, Cejudo.
Israel Adesanya, Edson Barboza, Kevin Lee, Jon Jones, Mike Perry, John Dodson, Johnny Walker, Eryk Anders, Yair Rodriguez, Dan Hooker, Alex Oliveira