Isley was launching explosive arrows that were leveling the entire countryside, and were able to follow the enemy. Also Isley in his awakened form has speed that is greater than that of Rigaldo. Plus Isley can keep fighting with half his body missing as if it were nothing.
I'm not sure the battle will be so simple as you say it is.
I do not remember enough to make a judgement, but if 1 can blow away landscapes with arrows... well he'd be a likely victor uneless they start close to each other.