This results in a full screen of fire that is pretty much unavoidable if you have to engage the elite as a melee.
To summarise, molten:
1. Does the most damage
2. Stacks several times
3. Is always on
4. Rate of ticks affected by fast affix?
That makes it pretty overpowered, and the Devs are comfortable with it. I have to disagree with its balance. You can outgear almost everything, but molten will still nail you time and again. That is even if you run, and do not stand in fire...just brushing by it takes off a more than decent amount of life.