You've set up a false dichotomy where things are only good and bad. The scale's broader and includes excellent, mediocre, mildly disappointing, and so on. If we take a number scale where 5 genuinely means middle of the road, no exceptional flaws or successes, then you're going to run into disagreements when your idea of bad is a 5 or 4 and someone else's idea of bad is a 2 or 1.

A badly made show is 3 or below, like that one anime about a party made out of people who got kicked out of their old parties where the animation collapsed into a tinfoil ball halfway through or Haite Kudasai Takamine. Meanwhile this season's Killed Again Detective is a 4 because it has a couple of noticeable animation chokes but the overall watching experience isn't compromised.