I haven't sat down and calculated it out but to me personally the hit to miss ratio was much better in those decades with more hits each season that would go on to run for several years and churn out consistently good high quality seasons before jumping the shark and ended up a mess in the final seasons(series finale). I just think the dramas, definitely the sitcoms were much better with the likes of Dallas, Hill Street Blues, NYPD Blue, Murder She Wrote, The Golden Girls, 3's Company, Empty Nest, Nurses, Friends, Roseanne etc. I even think the fact that there are so many shows resurrected this past decade from the 80s/90s speak to a desire by studios to recaptue the nostalgia and enjoyment of those programs--Melrose Place, 90210, Dallas, V, Bionic Woman, Knight Rider, Charlies Angels, Hawaii 5-0 etc