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.
it's partly true but you go too far imo in the idea that "you always get what you deserve".
Players can't have so much control, there's of course some luck involved (whoever the player I don't say that about Djokovic ; Fed, as I said before, and even Nadal -I remember some very important points where his ball hardly touched the line- have been lucky at times)