If a difference is consistently 5%, Patchwerk stats might start being unimportant compared to the mechanics of a spec. e.g. people slowly started moving towards Arcane from frost in HFC - before it was well ahead of DPS - because of the utility of single target on-demand damage and better control in some cases. In this case fire is a very convenient spec to start the expansion with because of the low effort it has to do decent AOE and single target simultaneously, so even if the difference was 0% it would be very hard to convince people to chance spec for 5mans or early raiding.