Mercer/Bannon/Trump and co. are super spreaders of misinformation. They happen to also use facebook, but I dont remember any issues of "fake news" in elections pre-2016/brexit. So no, its not inherent to the platform, only to the bad actors on it.
https://drum.lib.umd.edu/bitstream/handle/1903/11375/Misinfo...
Obama was probably the first candidate to win thanks to social media and facebook groups. Partisan Facebook groups post a lot and it's 50% your party's interpretation of reality, 45% outrageous claims, 5% pure fake news. I don't even think the fake news spreading is done maliciously, the groups are probably maintained by radicalised individuals who believe whatever news fit their narrative.
Trump (who often retweets fake news and even retweeted a website similar to the onion, once) equally calls fake news on opposing publications.
Still, I think fake news is a vastly overblown problem. Fake news is merely the scapegoat left wing media use to explain why Trump/Brexit won, even if it's represented so poorly in media. You can call it populism or far right extremism or Nazi, but outside of the rich tech community bubble, outside of universities, poor people want less government not more. The socialist message is lost on them, that's why Trump and Brexit won, despite the media coverage.
If we look at similar cases, like Berlusconi in Italy 30 years ago, it's just a matter of time before Trump understands fixing the government is hard, if not impossible and get caught in some corruption case himself.
The parasitical nature of the state just allow for the state to grow larger until it destroys its host. Spending in the USA is still at record highs.