If an expert player on average plays a 500 yard par five in 4.385 strokes, I believe it should be a par four. Given that the same player may play a 475 yard par four in roughly the same average these "half shots" should balance out.
The math there doesn't work out. If both of those holes are par four, then you're 0.385 strokes over par. They don't cancel each other out, they add to each other. You'd play two holes the "expert" plays in 8.77 but par would be 8.
"Expert" is a scratch golfer. PGA Tour pros are "better than expert."
This whole topic makes no sense to me. All you're doing is fictitiously changing the final score relative to par. Who cares? Is the 10th at Riviera going to be a par 3 suddenly, because pros can reach it? Why?
It's not like PGA Tour pros average 4.3 on par fives. Tiger Woods in 2000 still averaged 4.37, but second place was already at 4.5 (Robert Allenby of all people), and the median value that year was still 4.7 - so you'd round that to 5. And that was in 2000.
In 2017, the leader was Hideki at 4.48. The median was 4.67.
Artificially protecting "par" this way is no better than a golf course that tricks up something to protect par, or shortens a par five by 20 yards and calls it a par four. You're both doing the same thing - manipulating par. Just let the field make "birdies". Who cares?