That difference would be HUGE as it pertains to cosmological constants, the math behind so many theories.
We are talking vast distances here and just that much of a difference would cause many theories to be tossed out. It’s isn’t the fact that the percentage is small because on a grand scale small becomes large ... it is the fact that there is a difference at all.
Is it important to know? Absolutely. Is the reason for the photon delay important to know? Sure is. Will it destroy all known human knowledge of the universe to date? Hardly.
Nope. It wouldn’t.