"which is essentially the concept of the speed of light being the same in any reference frame expressed by math, that concept you claim it rejects cosmic redshift"

So why does it take longer to cross the reference frame that is the "expanding universe," causing cosmic redshift?

Doesn't that contradict the point you are making?

If the reference frame is expanding, than shouldn't the speed of light also expand/increase, in order to remain Constant?

What metric does the speed of light reference, if it's not space?

Einstein said, "Space is what you measure with a ruler."

What is the speed of light measuring, if it's something other than cosmic space?