"So according to YOU, and that inflation chart, I should be inflating those G rated tires at about 70 psi."
YEP, Add 5 psi to the chart.
No I am not the only person doing so.
My Avion had GY "E" tires inflated to 80psi. Changed toy to GY "G" because there were no acceptable US Made "E" tires at that time so I went to the GY "G" tires and the chart said 80 so i ran them at 85psi. Ran this for several years and thousands of miles with perfect tread wear and NEVER hot.
Charts are there for a reason.