Realista this is amazing! Thank you, I honestly did not think of the league average would make sense but it actually does! But even with excluding it and using your weighting, one could reach better rankings for each position.
For Mete, claiming that this is how player's contribute to a win does not make sense. Firstly, as serdar wrote, they call it something else. Secondly, is number of aces how a player contributes most to a set win? I mean you can make 4 serve aces and then receive terrible and kill 1/10, but still get a good grade in this ranking and you simply don't contribute at all. After all, my weighting would be very subjective too but I guess best option is to make a questionnaire to coaches and ask them to rank different actions for each role, for example for OH, they can rank serving, receiving, digs, attacking and blocking. With that, we might at least get a better weighting for each position and therefore a better ranking of players.