Your main stat shows your damage, while other stats show defense (there should also be defense for main stat but apparently it's not shown anywhere? idk how that works)

From there, it's pretty straightforward - subtract their defense from your damage and you get the number. 6488-1682=4806, which is the damage you do. Now, with 20% rock-paper-scissors bonus, he does 6315*1.2-1318=6260 damage.

They're trying to make it more interesting than just plain stats, but currently they're failing at it pretty hard. Outstatting everyone is your best bet.