The only valid argument against using step 2 as the main numerical objective value in ERAS is the one
@AnatomyGrey12 has pointed out, which is that if we use step 2, then it throws off peoples timelines if they don't do as well on it as expected and thus, can't apply to neurosurg or whatever competitive specialty that they had planned. But IMO, I don't think that is that big of a deal. I mean if you aren't planning for backups already then you're making a mistake at it is.
I don't see the problem with f/p/hp or quartiles for step 1, then have step 2 become the more important exam, which forces us to take it earlier than normal (Spring/early summer of third year), which means you have your score well before ERAS opens. And if you're a borderline student, it would be wise to have backups in place for an application if something goes wrong on your ortho app bc of Step 2 score. This seems to be a semi decent change if the NBME is dead set on making some change. Students from non-big name schools still have the chance to crush step 2, and also get high pass on step 1.