I think the prematch is somewhat unfair to US students. One can't deny that these students (IMG, FMG and DO too) are taking spots in some competitive specialties like anesthesia, ER, etc. that many US grads would like to take...many equally qualified US grads. As far as what type of physicians they make, I've only trained at hospitals I consider to be good...and any DO/IMG/FMG people there were equally qualified and functioned as well as others...small caveat is that a few seem to have problems with English which impair them somewhat...mainly in regards to doctor/patient communication.
I think the prematch should be done away with, and there should be a 2nd match (instead of that stupid scramble). At least for intern spots, I think there should be only one match and no back door deals/prematches. This would be bad for people who finish off-cycle, though...right now that is mostly Caribbean grads, but not ONLY.
The issue of who pays for residents' salaries (US taxpayers, ultimately...) is also relevant, I think. I doubt that most other countries would use their tax revenues to pay for US born, US trained docs to go over there and train.
One the FMG/IMG/DO gets to my hospital, I am equal opportunity. Most people will not care where you are from if you can do your job.
I think there is some truth in the contention that Caribbean schools do more board prep, and/or allow more time to study for boards. We had 2-3 weeks maybe to cram for step 1, after getting reamed with multiple hard blocks/classes and exams at the end of 2nd year of med school. I think that a lot of the Caribbean schools realize that their students are at a disadvantage and they NEED to do well on boards, thus will allow students,or even force them, to do more prep for Step 1. Also, some students are in the Caribbean because they aren't good at standardized tests, at least in part, and their schools know that. It doesn't mean they won't be good doctors, but I think it's a fact.