I’ve experience some of the mind-numbingly slowest checkers being obese black women who barely seem to have enough energy to keep their balance and breathe. Let alone grab a bit of merchandise and slide it past the bar-code reader.
OTOH, one of the quickest food service employees ever was a young black man who worked in our base restaurant. He could roll up a burrito is just a few seconds and it was perfect. After your 2nd or 3rd visit he already knew your standard order so if you wanted to vary it you had to be quick to let him know.