Mr. Plummer has two original designs that deserve consideration in the second 50- Preston Trail and Champions- Cypress Creek. I like Southern Hills better than either, and even with Press' nine at Prairie Dunes and the horrible gunch, I liked that one more as well. Of course, having superior topography (both courses) and a sand base have absolutely nothing to do with the quality of the course.
Ralph Plummer was primarily a Texas architect where he apparently got enough work to make a living even during the Great Depression. Perhaps Perry Maxwell was so highly regarded that he was pulled to the places you noted to work under the guidance of someone else. Or maybe he had to chase deals to put food on the table.
Plummer had a very large hand in the three courses in Texas that have held the US Open- Champions, Colonial (he built it for Bredemus - two major tournament winners who knew Plummer intimately and a high ranking official at the club told me that Plummer did much of the design work there as well- and yes, I know that Maxwell was brought in post flood to work on three or four holes), and Northwood. His body of work of nearly 100 courses is largely intact today and is enjoyed by tens of thousands, mostly at very affordable prices. He may not be a rock star among the gca aficionados like Maxwell, but his work doesn't take a back seat, at least not in my admittedly limited perspective.