I disagree that black mirror has to save the world. Art doesn't have to literally save the world to be useful, it just has to add to the conversation. The fact we are talking about it proves that it has.
On the other hand, i've never really liked black mirror that much. It feels polemical to me. Its unrelenting pessimism robs it of nuance, which makes it feel flat to me. To be clear it doesn't have to be happy, it can still be grim and dark, but when every character is a terrible character, it undermines the story
Take the episode "nosedive" where everyone is obsessed with social media ratings. Compare it to other people who copied it (meow meow beans in community, or majority rule in the orvile). I think the other tv shows did it better and honestly made technology look worse, because they had characters that weren't cartoon villians.
Maybe the part i don't like about black mirror is not that it showd technology stripping people of their hummanity but that all its characters already lack humanity so there is nothing to strip, which is kind of boring.