Inappropriate for obtaining unbiased confidence intervals, yes, but this doesn't matter for ranking if bias is uniform across everything that's being rated.
You make a good point that there might be differential bias depending on when the movie came out, but I don't think the solution is then to say "well, now all bets are off, might as well concoct our own techniques and assume they're just as good or better." Statistical techniques are not either fully valid or fully invalid. Simulate the bias and look at exactly how it influences the results of a particular technique, and then perhaps use that to make an adjustment based on data rather than intuition.
You make a good point that there might be differential bias depending on when the movie came out, but I don't think the solution is then to say "well, now all bets are off, might as well concoct our own techniques and assume they're just as good or better." Statistical techniques are not either fully valid or fully invalid. Simulate the bias and look at exactly how it influences the results of a particular technique, and then perhaps use that to make an adjustment based on data rather than intuition.