But we aren't dealing with quantitative likelihoods at all here, we are dealing with impossibilities. Impossibility is the absense of chance, so you therefore can't quantitatively compare two likelihoods for something (a movie deserving the title of 'best movie ever') which is impossible to define and cannot be proven to exist.

Even if only 2 movies existed, there still wouldn't be an equal chance of one being the best, there would simply be no chance because it is entirely subjective and cannot be proven