Deathfire seriously needs to do its damage over a shorter duration
Something like 2 seconds. And then Riot can find some way to make DoT effects only proc the thing once because otherwise that nonsense gets silly. They managed to make Malz' E only count as one spell for Thunderlord's, so I figure they can pull it off.
Why?
Because as it stands right now, the amount of damage Deathfire deals over the time-frame of two Thunderlord's procs is pretty darn similar. If two Burst procs are dealing just as much damage as reapplying Burns over the same time, then there's absolutely no reason to go with the Burn damage ever The Burst typically requires less commitment and personal danger. This is going to get worse when the change to Thunderlord's goes live since it'll scale down to a 15 second cooldown later in the game.
So yeah. Deals damage over 2 seconds instead of 4. DoTs only count as one spell. Make it happen Riot.