Only burn effect that needed a nerf is Lave Golem´s, because it was bumped from 700 in the anime to 1000 in the TCG; most likely to make it blend better in an 8000 LP format. Since in DL we have 4000 LP, that I understand.
But this one, for example? It did 500 points of damage in the anime. Again, a 4000 LP format. Should deal 500 in DL, too.
Remember that anime characters have more restricted card pool. They're restricted by what the duel planner in the production team gave them.
That's why burn cards in anime doesn't seem to be as OP as in real life. The cards that would make them OP as a deck are not there. When you apply real life deck building to them though, then you'll realize there are combinations that can make them OP.
But that's supposed to be the main appeal of Volcanics. Going into the offensive, disrupting board, and if your opponent turtles, you punish him with burn damage. Nerfing that aspect of theirs is stiffling their very design.