If you look at the data you can see the 95th percentile log for fire is the rank 1 log v the rank 200 log for arcane. Look at "Max" to see what i'm talking about, fire will stay still while arcane and frost surpass it.
It should be mentioned that fire isn't that far behind arcane and frost on ST, it's just most people play what is best, regardless of whether they have to or not.