Fiends are hard enough as it is, Fire fiends are worse, trying to bomb one of the hardest common enemies in the game while having the formerly captive knights knocking devilites out of your bomb range is just...... I have words but I can't say them....
Honestly, I'd rather have a full team of Fallen sets spamming Acheron charges than these Bozos, at least they would deal some damage and could actually listen when I say don't "knock stuff out of my bomb range".
It is horribly annoying to see a devilite about to take a blast only to have "the stupid knight" knock it just out of range (but still a close enough range than you don't have time to react to the pitchforks they fling at you).......WHY ARE WE SAVING THESE IDIOTS?!?!
Lol i thought i was the only one who hated those NPC's because i bomb fiends too, but unlike you i find it easy to bomb them with a DBB unless those useless knights come and send them away with their swords. Anyway, have you tried using a Voltaic Tempest before starting the DBB chain? It helps a bit.