corner and specifically outside corner is the most athletically demanding position in football, since you have to react on a dime, and have to defend against double moves. you need fluid hips
to change direction suddenly and move laterally and you also need elite acceleration/agility to recover
there are a few exceptions with press man corners and zone-dominant corners who win with physicality, positioning, leverage and smarts but they are pretty rare and they still need some baseline athleticism
white DBs usually dont have that combination of athleticism and fluidity. hence why they're usually put at safety where they dont have to move laterally a lot to get turned around, and mostly attack downfield
with cooper theres no doubt about his raw athletic ability, but fluidity is still a big question mark