You seem to be forgetting the 10 years that passed between the C5 RS6 and C7 S6... The standard of performance has moved on, which is "progress" in most people's books. That's why a C7 RS6 or RS7 is SO much quicker/faster than the C5 - that's progress.
RS6s/RS7s with tunes run mid 10s, while S6s with tunes run mid-11s, so the performance gap between them remains - "...same as it ever was". (/Talking Heads)