Or do both! I primarily train Muay Thai these days, but I mix in two minimalist kettlebell strength sessions per week. 20 minutes of emom double kettlebell ABCs with some sets of pull-ups at the end keeps me in zone 3-4. So I'm getting some cardio conditioning while doing my strength training. Sure, it's hard to overload at a certain point with kettlebells, but making a goal to be able to OHP double 24kg bells will get most people pretty far.