To be honest, spell OTK was OP before, not to mention Fire also has Fahrenheit, which gets out of control. Now that it requires 6 cards, it has a similar card requirement of that of a Dragon-Chimera OTK. Seems fair enough to me.
(Also, wasn't there a touch of reason when Arena went all haywire? Iirc, practically all the hacked decks were 2000+ marks of Fire with Bolts and Fahrenheit.)