“BTW, I am convinced that the speed of light has slowed “
Hasn’t that already been proven with atomic clocks at higher altitudes? Like if you take the slow down and calculate the span of the universe what you see is 14 billion years of time/age, but it is actually 6,000 years old due to slowing of time?
I see what you are doing here; but it is the SPEED of the clocks that shift the time.
https://en.wikipedia.org/wiki/Time_dilation