Sven — A "myth" is usually involving the supernatural. I'm not sure the total numbers of bunkers at Oakmont in days gone bye is a "myth" as much as it is a trivial fact that we just can't seem to answer now in 2021. If you heard Arthur A. Snyder discuss building bunkers every day for many years (under the direction of Mr. Fownes), I think you might come away with the feeling that the place was littered with "pits" of all sizes, shapes an locations — and there did not seem to be any limitation, budget constraints or appetite for building fewer as opposed to more. (Arthur A. Snyder, by the way, began his time at Oakmont in 1907 caddying for Mr. Fownes. After that, and getting to know Mr. Fownes, his interest in greenkeeping landed him a job on the grounds crew. Some years later he left Oakmont to pursue a career as a superintendent. In 1979 Arthur A. Snyder became the 19th recipient of the USGA's Green Section Award.)
Besides, as Desmond Muirhead once said, "A golf course is a difficult thing for most people to appreciate as a whole — the key to understanding any course is to study each hole individually...a single hole is much more apt to be 'solved' as opposed to attempting 18-holes in one single dose."
I've used a similar notion — "When a players gets too many holes in their head...it leads to disarray."