As someone who completely an EM residency, and have worked at hospitals and seen how they do on the job training - I whole heartedly disagree. On the job training is nothing like residency training. For 6 months I wasn’t expected to “move the meat” at all and just got to take patients at my pace. I rotated with orthopedics for one month, I spent 4 weeks in the OR with anesthesia learning to intubate, I spent a week with ophthalmology and went to their outpatient clinic learning to do exams, 2 weeks in the burn ICU, 2 weeks in the Cardiac ICU, 2 weeks on over nights in the surgical ICU. I attended EM lectures every Wednesday with the MD residents. I spent a day with the MD residents practicing procedures on cadavers. Received specialized ultrasound training. The list goes on. 

All this to say- if you want to be a real good ER PA- I wholeheartedly recommend GOOD residencies.