Neutral mutations are “not necessarily destructive”? No, they are absolutely neutral, neither an asset or a detriment; thus neutral. This advances the theory because it shows how selection works on some DNA but not other sections.
ERV’s do support common ancestry. Finally you got something correct. How you think this isn't a Scientific advancement of the theory of evolution through natural selection I do not fathom, it is supporting evidence for the theory of evolution that the remnants of our common ancestry are there in the genome, subject to the neutral mutation rate.