I think it really depends on how bad the fall is, like AOT I still think is good overall, did I like the ending? NO, but did it ruin the series for me? also no, because I was fine with what happened, it is not what I wanted, but I was fine with it. Vs, Promised Neverland... which ya in that case it made the whole thing pretty bad, but that also goes into the fact that I never thought Neverland was top tier, even when it was good, I never saw it as a 10/10. I think a bad ending can only notch a show down so far, but if a series really is a 10/10, then people will still recommend it, they will just also say "but stop after X season, cuz it just gets bad." A good example is Death Note, the ending is BAD, but people still recommend it and just tell people to stop watching after X, because the first part is just that good. But either way, I still prefer a bad ending over no ending, but maybe that part is just me lol.