I think I agree with you that par 3 holes do not, by themselves, differentiate good from great courses. However, while I think some architects do/did not rout the courses with them foremost in mind and did not emphasize the design par 3s as being important and highly interesting, they are usually more memorable than most holes to average and interested players. Some architects did not dismiss their importance and some were critical to the greatness of the course. In my experience, I think Rolling Green, Cypress Point, Shinnecock Hills, Philadelphia Country, Somerset Hills, NGLA (2 out of 3 great par 3s), Maidstone and others are examples of this.