People that are not seeing the benefit of this merger or think that DOs will have a harder time in certain specialties are misguided.
Many of the most competitive DO applicants going the AOA for specialties like ortho, ENT, NS, uro, optho, and derm have high USMLE scores or COMLEX scores in the same percentile as MDs matching in those respective ACGME specialties. It was possible that many of these DO applicants would have been able to match ACGME in those surgical specialties or at solid ACGME IM, EM, rads, anesth programs but choose the AOA route because of the gamble of opting out of the AOA match. Now that there is one match, competitive DO applicants can apply broader and potentially match at a broader array of programs. Avoiding the hassle and gamble of two matches is HUGE. Will academic IM residencies with years of DO bias like NYU still be off the table? Most likely they will be, but many other opportunities will be available.
Furthermore, this increases fellowship opportunities for all DOs that would have gone to AOA residencies. All DOs can now go for fellowships if they are qualified and are accepted. This benefits every DO -- ranging from a DO orthopod can now specialize in hand if they are qualified and someone who was going to go AOA FM can specialize in sports medicine in many, many more locations.
No one with any common sense thinks its going to magically make everyone competitive everywhere, but it opens up a lot of possibilities and competition. Additionally, just like how many MDs look down on DOs, DO PDs at the competitive residency programs will surely still be taking DO students. In addition to the traditionally AOA accredited programs, DOs can take the gamble to apply to ACGME programs that could have potentially matched at but deemed too risky with a dual match.