Seeing as it's highly difficult and improbable to approximate or come even close to kred board stats with bikes (the only things bikes good for are transit and access to storage as in Rw3's) hence, they are not normally meant to be an attack accessory.

Which makes me wonder why they don't have defensive stats like evasion, flee rate, defense rate, and hp restore option scrolls?

Would suggest at least those. Just my take on bike slotting.