I am one person who would rather not see gunpowder in a fantasy setting unless it is used exclusively as an explosive bomb by siege engineers.
Agreed, thats the only use of gunpowder in LOTR and they actually pulled it off quite well.
Also the ranged arguement you provided was good to know
and yeah as long as they cant make godly heros or at least not an army of them (as seen in LOTR...) then it should be alright... im guessing that the general rules apply? cavalry < spears < infantry < archers < cavalry