I think “mediocre” in this context would be mediocre to most people.

I think you cannot ask about something subjective without getting people's personal opinions. If you ask about an aspect of a mediocre thing, then you can expect at least some debate about what counts as mediocre, and probably none of the people's answers will be correct.

For me, a "mediocre" movie would be something that I would only watch again if a friend wanted to watch it, but if it was just an option and I got to choose, I'd never choose it. But if it was just "on", I might not change the channel. Let's see, like The Rock directed by Michael Bay.

And then there are "bad" movies that I wouldn't watch even if I had a friend who wanted to see it, like any other Michael Bay movie that I've seen. Armageddon had pretty good music, but it wasn't mediocre. It was bad.