Why is Darmanitan almost never used outside of Sun teams? It shares many similarities with his broken Galarian form. Its Flare Blitz hits harder than
G-Darm's Icicle Crash and it has the same speed, eq, u-turn etc. It can also more viably run HDB i guess. Is the typing difference or power what makes regular Darmanitan non-standard?
Adding to the great answer above, Darmanitan is much less powerful overall compared to its Galarian counterpart, it pretty much relies on Flare Blitz to deal consistently high amounts of damage and alongside its susceptibility to hazards means that it's going to kill itself faster before it gets a kill itself. It's just a very high risk Pokemon with very little reward because offensively what it gives is very barren outside of sun teams, which are pretty niche all things considered.