If there was something wrong with how Par was assessed when building and playing golf courses, something drastic would have been done within the last 400 years.
Under "normal" or "common" playing conditions Par
3s are any yardage up to what Jim Furyk hits 3-wood.
4s are up to Jim Furyk's driver plus Jim Furyk's 3 iron.
and 5s are anything more than that to a reasonable point.
I use Jim Furyk because the guy hits the ball so straight and solidly. So, it's reasonable to assume that anyone who hits the ball farther than Jim may stray offline to give each shot more value than just distance.
The 8th at Oakmont I think is the perfect example of what a long par 3 should be, and anything more probably blurs the line. I know he hit 3-wood there at least one of those days. It may be longer than Jim's typical 3 wood, but the course was firm and the ball releases on greens that are stimped at 14.
Obviously not all people should play the "Furyk" tees
.