Lmao. Well now i know that also! I got a shield earlier tiday and thought my struggle was over. It rolled with three seperate sub stats. All i needed was double speed and the ordeal was over. Back to prayers to the RNG gods i guess .
Something else to note - substats scale based on their rank. 6* gear will give you more speed than 5* gear.
AKA - try not to upgrade 5* gear :)