Other thing is - even with a good hit where you don't break your own leg - what good does a lower leg kick do?
A hard kick to the meaty outer thigh has your opponent hopping on one leg. Sure - a kick to the lower leg is painful but with all the adrenalin running during a fight - you don't feel that sort of pain till the fight is over.
Yes, but you're always going to have pain after a fight. It may be your upper or lower body, but something is going to hurt.
With leg kicks it's all about timing and point of contact. Good leg defense, the sort you see at Muay Thai, is the one that welcomes legs to the outer or inner part of the leg with your knee. Trust me, if the other guy hits you in the knee once, he will not try that kick again. Hence his leg offense will either switch to the upper body or stop altogether. If the leg offense goes to the upper body, welcome the kicks with your elbow to the shin. Your elbow IS NOT going to break. Good offense means knowing when to kick effectively, which takes a lot of time to master.
CroCop was a good example of how effective good leg skills can be (defense and offense): Dude was knocking the fuck out of people twice his weight (Sapp,) which makes it the more bizarre how fighters did not and do not even try to go down that road.