Most cases are simple, most general dentists can do things with experience and CE. The complex patients take much longer which means reimbursement is lower. At my school perio and prosth both place implants, with prosth doing all on 4s, full arch stuff, etc. I am not going to say what is best for the patient, what we should do ethically, how we can be the best trained, etc. Because the answer for that is obvious (full MD/ACGME accredidation). However, you will not attract the best applicants if your specialty is almost double the length of other specialties with the same or lower salary. The fact is the majority of OMFS applicants (and surgeons) are not die-hard academics.
There's a reason H&N is not very popular in ENT, with approx. 50% of spots going unmatched each year. Things like QOL, salary, time spent training, do matter to many people.
ENT, PRS, and Uro are only 5 years not 6, unless you don't match the 1st time.