Swampthing...
I used to shoot very heavy bows all the time...over 80# and shot heavy arrows to match...over 750 gr. and liked it. When I decided a few years ago to lighten my bow weight to maximize my shooting years, I was stuck with alot of heavy arrow shafts. I shot shafts around 700 gr. out of my 64# bows and they shot great. However, in re-reading Hill's book and reading Schulz's Straight Shooting and realizing the same info you did, I lightened my arrows to around 550 gr. with lighter heads. The last few years I've been amazed at the penetration I've gotten...really good...but my arrows are also getting downrange quicker with a flatter trajectory. My bows don't feel shocky at all either.
This leads me to surmise in my opinion for my circumstances.... A)a well built American Semilongbow doesn't need heavy arrows to shoot well or less shocky (heavy arrows might in fact hide some tillering problems or shooting form issues) B) flatter trajectory leads to better shooting at all distances C) an arrow of 500 - 600 grains is plenty out of any modern bow for all game up to moose on our continent (African/Australian game is the exception possibly) D) before the heavy arrow or efoc being forced upon us in the last few years, game animals all over the world were being shot very effectively with longbows (and recurves) by big name bowhunters like Stevenson, Hill, Swinehart, Bear, Pearson, Schulz, Dougherty, Eichler, et al.... I believe there is a middle of the road approach.
I also believe that Schulz said it very well...as you quoted earlier.