I think perhaps the reason PSA is such a mix is it was an attempt at reforming doctrines that were not exactly worked out (at least to a degree one would consider it "biblical" or from Scripture itself). All PSA does, ultimately, is substitute justice for honor in the pre-16th century RCC view. BUT being Protestant it has additional assumptions which it cannot meet (like sola scriptura). In the end PSA is held on faith, not in God or Scripture but in the Reformed Tradition.
I think that most of us hold some things this way, but hopefully we reexamine those views and either hold them legitimately or change them. As a child I was taught a doctrine of the Trinity. I can't say I understood it back then. After studying I now have a more firm grasp on that doctrine and can call it my own.
Perhaps PSA is like that. It is a corrupt mixture of secular philosophy, RCC religious thought, and Scripture. I think it was worked out well enough for its time (at the beginning of the period) but by now it should have been corrected. That said, it is not the worst way to start. The gospel still shines through, not because of PSA but despite it.
