During a preignition event, the valve temperature is rising at the alarming rate of as much as 2 degrees per second. While this is happening, the EGT is going down significantly.
During detonation, EGT moves little or goes down slightly while exhaust valve temp goes steadily up.
How can that be if EGT affects valve temperature?
The correct observation that EGT and valve temp go up as the mixture is leaned from full rich to about 25dF ROP is the red herring. It's a correct observation with a misapplied causality.
We can hold the EGT steady on the test stand and reduce CHT and the valve temp goes down. We can raise the CHT and while holding the EGT steady and the valve temp goes up. If we hold the CHT steady and alter the EGT, the valve temp remains steady. Explain that and continue to insist that valve temp is related to EGT.
One other thing. As I have spent the last 15+ years studying this stuff, I have had to unlearn what I knew to be true, but wasn't. It was not a comfortable feeling.