They changed the way this works though. The number of attack & defense for a player in your top squad doesn't count anymore. I can have 17/17 top squad all with attack/defense 100/100 and my current strength is exactly the same when I replace them all with brand new players with an attack/defense of 10/1 - I've swapped them all out & my current strength only changes when I up my own attack/defense with skill points.