When I start the Devils Lair I switch to a overload sword and kill him real quick. Then I switch to another power weapon and continue. Problem solved and it only takes a few seconds

Rush it and kill it yourself Problem solved

At the difficulty you are doing them it doesn't change much Try At least legend...or master if you feel frisky

You’re doing Hero NF’s. The drop chances for a NF weapon at that difficulty are abysmal so it’s not even worth killing that first champ. If killing the first champ is that important to you, you’re free to kill the champ yourself. If you’re going for NF weapons, do the NF on a higher difficulty for a higher chance at getting a NF weapon.