You sure have a different version of what fire was in Legion! Spec was bad w/o pryo bracers and even then it was PRAY the RNG Gods gave you the damn procs at the right time. Frost is in similar place currently with BF procs, number of times you have to cast 8+ FB's to see a BF proc is silly. When that happens kiss your DPS goodbye.
It was only king when the stars aligned after they nerfed the crit passive, aka people saw a fire mage with a ridiculous parse but failed to notice the 100,000+ other parses that weren't even in the same ballpark.