Or its like a u throw a dice and got 3 and u got re roll ( means u get another chance to roll dice) now if u get 2 in ur second chance, than u get 3 as it was best result or suppose u get 5 in second chance than u will get 5 as result.
Best result out of 2 will be given as reward.
In case of arcane u got 6 in ur first dice throw....so it do not matter u throw dice twice thrice or whatever cause 6 is max reward u could have ever got.
So re roll won't work on arcane rarity