Especially towards the end here, very specific combinations of azerite traits, corruption effects, and essences could have synergistic effects in the simulator that the optimizer doesn’t predict.
In your case, if you start playing around with things, you’ll see that your equipped gear seems to be pretty specific… if you change one of the essences or one of the corrupted items or one of the azerite traits, DPS seems to drop. I’d have to spend a lot more time trying to figure out specifically why your equipped gear simulates better than setups that are barely different.
One thing we did for fire mages is favor 3x blaster master when you have hyperthread wristwraps – but since you don’t, some of that optimizer logic is not kicking in. Since that build was so dominant, we narrowed in on it a bit.
In general this is pretty rare – that a specific synergy will spike like that and that the optimizer won’t agree with the simulator on it. With Shadowlands we’re taking a slightly different approach with the optimizer that should handle this sort of thing better if/when it comes up as the expansion goes on. Towards the beginning it shouldn’t be an issue because gear is simpler.