It's clear you don't know anything about physics. Look up 'Lyman Alpha Line' and get back to me. Light from stars has distinctive spectral lines that are still obvious even when red-shifted.
Despite your gross condescension, I will attempt a response (notwithstanding I don't belong in the same conversation with someone so intellectually and scientifically astute as yourself).
I am NOT asserting that we don't have the ability to measure spectral qualities and quantities of distant objects. We do.
I am merely stipulating that, perhaps, we have no way of assuming, much less knowing, what spectral qualities a particular galaxy OUGHT to present.
And, while it is clear that you probably have some pretty good talking points up your astrophysics, it is even more clear that you don't have a clue about polite dialogue, which is quite typical of know-it-alls.
So I will give you the argument, as it has been aborted by your causticity.