I think it will be easier if you just set it to the lowest possible item level for each one instead (like the current item&level sync feature). That way you don't have to keep updating the stats when you update (since it's going to be super cheap to rehash old fights).

Also, I don't see how this is appealing at all unless it gives as much reward as 5 trials or more. Maybe if you can guarantee 4 special drops (like mog whiskers if King Moogle pops) or something for each primal, it might work.