You are probably right about the effort thing, but LeBron is much bigger and stronger, and has similar quickness. At his peak when the effort was there, he was better than Kobe because of his versatility and his length advantage. Bottom line, once you got a certain age something has to give. LeBron is there now for sure, but Kobe was pretty bad defensively toward the end, and not great in Season 15. I am sure Kobe never gave up on plays Like LBJ does from time to time, but he also wasn't capable of locking down all stars in year 15. LeBron still can, although for limited stretches only now.