nope lol the rook in the main team isn't slow as heck, now their not as fast as knights, they can't just disappear from sight from moving incredibly fast. Because of becoming a devil all the humans have their 5 senses increased, and their entire physical attributes all of them increased more than normal, the 'Devil Piece' just gives them a bonus to a certain attribute basically. 

so it's not like their super slow or anything.