If a let cord turns into a winning shot, it is because the shot was good enough to go over the net despite the fact that it hit the net. Luck has nothing to do with it. If the ball does not go over the net it is because the shot was not hit well enough to do so, whether it hit the net or not.
If the shot was good enough, it would not have hit the net.
Do you play sports? I'm not saying that luck is the only factor, it's a big factor. Skill (talent, physical, mental), is of course a bigger factor than luck. But when the skills are almost even, like top players today, a lot of time it was decided by luck. Daily form also depends a lot on luck. Sometimes your game just doesn't click one day, and in full flight in the next.
No lucky club player will ever beat a serious prime Djokovic. Unless Djokovic rolled his ankle mid-match. If that happens, what do you call it? Djokovic was not good enough, because if he was, he would never hurt his ankle?