APA accreditation has always been meant as a minimal standard; it's something programs should achieve and then exceed, which unfortunately seems to have stopped occurring. Simply because a doctoral program meets APA accred criteria doesn't necessarily mean people won't qualify it as a "diploma mill." The term is used to describe programs that, in general, are thought to have reduced admissions standards, large class sizes, and poorer objective and subjective student outcomes on the average. APA accreditation isn't doing a good job of stopping this from happening.
As for TA/RAships, I'm curious what you think a fair wage would be? If you remove the tuition waiver (which, for out-of-state students, which is what the majority of graduate students seem to be at these programs, includes in-state tuition status), the typical pay I've see would probably be in the low- to mid-30's. For an individuals with a bachelor's degree in psychology, and for a 20-hour/week commitment, that seems fair to me. Even not counting the tuition remission, the pay is actually rather similar to that of an adjunct professor brought in to teach a course, with the workload for the TA/RA-specific duties being similar or less. Do graduate students work long hours? At times, but that doesn't mean the long hours are necessarily directly related to their assistantships (which, again, are technically capped at 20 hours/week); they're usually related to classes, clinical work, and research in addition to the TA/RA duties. Ultimately, these students are also learning; that is, they're being paid to go to school.
I don't know if anyone has done a study of the mean and modal number of hours worked by students in different types of programs, but I'm not sure that it would differ very much. Then again, if I could choose between no to moderate-debt coupled with a 50-60 hour work week at a funded program vs. a 40-hour work week coupled with $150-200k in debt, I know which option I'd choose.