Interesting discussion. But the improved efficiency isn't all that great in practice for 1/10 scale. HV would of course be theoretically somewhat more efficient for the average guy done correctly, but it wouldn't reduce the load on the battery much, well, assuming the same size overall pack. Yes, the amps go down, but now each cell is smaller, and thus has less current capability. The slight improvement in efficiency which would help the battery some would be offset to some degree by the reduced packaging efficiency of the battery with more cells/connections. So you are pretty much back to where you started for the battery.
Same principle applies to some degree to the motor wiring. To make the speed reasonable would require higher turn motors if I'm not mistaken. That probably means smaller wires that have less current capablity. And thus offsetting some of the efficiency increase and possible heat reduction.
BTW, most guys don't use 3.5 motors, so the excessive heat only impacts the fringe. And if we go to higher volts, with new less current capable escs, motors, and wiring, then the guys pushing the edge will still be in the same boat.
You say your stuff runs real cool, I don't doubt that a bit. So does my 2s brushless stuff, hardly gets warm at all, battery, motor and ESC.
As far as stressed out electronics, I still race one ESC that is nearly 20 years old, was 3 until recently when I started getting into brushless, with no issues at all. I have 7 in total that are 17+ years old, no issues.
And also consider safety, and the fact that kids, big & little, play with these things. A critical consideration as you go way up in voltage, especially with DC systems.
Once again, good Engineering requires balancing many factors. You have a valid theorectical point, but are focused on only one factor of a complex equation. Other factors need to be considered in the real world.
That said, enjoy your setups, just don't expect everybody to join in.