I get what you mean.
But in Swedish there is a saying that I think is relevant in this context that goes "många bäckar små gör en stor å", it roughly translate to "Many small streams can join up to make a great river". I believe there is an old Scottish saying with an equivalent meaning that goes "many a little makes a mickle", I also remember reading a saying that roughly goes "'look after the pennies, and the pounds will look after themselves".
My point is just, I believe that you can make tests showing that nothing matters. But yet, I strongly believe that everything matters. Like take away 3 good players from your roster and replace them with 3 players with 1-2 fewer stars, and its possible that your team still will perform great. Still, ability matters. It definitely matters if you have a 6 or 5 star team. Right?
My advice in relation to the above is definitely to be a perfectionist, take care of everything that you can take care of and it -- will -- show in the end. Or what do you think?