La Purisima is vastly under-appreciated by a great many people. I'd say it can rightly lay claim to a top three public position among the various open to the public courses I've played in the region. Play there in any afternoon when the wind picks up and you'll have all you can handle.
If difficulty was the litmus test for quality, then I'd more likely agree with you on this, but then you'd have to include the Babe on your list as well.
La Purisima is a course that I LOVED the first time I played it, but since then have grown to think less of. It's still a good course, and better than it's sister course (Hunter Ranch) but I think it benefits most from good conditioning and a remote and beautiful setting.
I don't remember the hole numbers, but the interior holes of the back nine are borderline awful - I think 13 and maybe 15 (the par 5 along the ridge) are horrific holes, and the tee shots are mostly an awkward bunch with several forced layups. I think 4, 8, 9, 11 (dogleg right) and 17 are excellent holes.
I agree with you that it's underappreciated by many, but I do also believe its overappreciated by a fair share of people too. It's a good, solid layout that I wouldn't send someone visiting from the east coast to unless they happened to be planning a night in Solvang or Buellton.