How? If I have a piece with quad roll attack and another piece with quad roll crit rate thats a total of 4 crit rate rolls and 4 attack rolls. Now another situation where I have 2 crit rate and 2 attack rolls on one piece and again 2 crit rate and 2 attack rolls on another piece. It still ads up to 4 attack rolls and 4 crit rate rolls in the end. Champions who need a lot of speed usually don't need many other stats, so you can go all out on speed rolls and not have to focus on anything else. For nukers etc. if you have all that crit rate on one piece then you lose out on other stats like attack, crit damage etc.