The case would depend entirely on how Fantano's business is affected in the aftermath. If his income takes a hit then he pretty much has the holy trinity of a defamation suit: a third-party published the piece (it wasn't written by Marcus on his own blog, an editor et al. signed off on it), he pointed out the falsehoods in the article with great detail in the response video and description alone (but could certainly go into further detail for a court of law), and loss of income brought about specifically after the publication of the article.
The article was a misfire. Someone tasked with taking down and/or exposing Fantano should have taken much more care on the matter to make sure this sort of mess couldn't so easily happen. This thread proves that Fantano himself has provided virtually all of the ammo you needed via his Twitter timeline alone.
Actual malice probably applies here as Fantano is a celebrity,and he can't deny that, there are articles after articles calling him the most popular music reviewer for example
With actual malice he'd have to prove the author knew it was false or acted with reckless disregard... The article is not great but the crux of the story: Fantano's side channel appeal to the alt right is not necessarily false and in fact in my own research I've seen a good number of tweets and reddit posts from in and around the time (and after) he started the meme channel that all express concern and disappointment that Fantano was doing things that seemed to appeal to that sort of alt-right audience. Some of the examples were not the best, but his association with known anti-feminists, known bigots, his defense of them, and even for example when Sam Hyde expressed his approval of the video he did with Amazing Athiest and Sargon and Fantano accepted that thanks would work against him. All these can be used to show that while potentially not all the examples are the best, the general thesis cannot be proven to be so clearly false that the author knew it or was reckless about it.
Some of Fantano's own words can be used to undercut a libel lawsuit. He himself claims the biggest issue was the part on Sam Hyde where he's accused of laughing... which he did, now he claims it's nervous laughter (which maybe it is) but he'd have to prove that there is no way the author could have thought it was anything else, and good luck with that, especially when in the video he defends Hyde's comment as it being just a joke and I can find a video of Fantano calling Hyde a comedic genius who he has no problems associating himself with despite having different opinions (which in the video is literally Hyde financially giving aid to the Daily Stormer, a neonazi website). He'd probably try to point to the rape element of the Hyde story too, but the defense to that is that "nailed" is absolutely a word often used to describe sex and that the author of the article did relatively quickly take it out (that and the "joke" is still about horrific assault and murder of Lena Dunahm so the rape element doesn't fundamentally alter the horrific nature of the joke).
He's also wrong that there was no way he could have known about Sam Hyde's political beliefs, that's not true as there were stories out there about him, about what the racist stunt he pulled at Yale for example, that and in 2017 Fantano defends associating himself with Hyde regardless so you can't even argue he wouldn't have done it had he known.
He can't even fully claim satire as a defense of anyone calling his videos sincere, because he made at least one video that was decisively not satirical (the one with AA and Sargon and a bunch of folks who are on the record as anti-feminists, virulent bigots, etc... )where he told feminists to rink bleach) so how can anyone who watches that then be faulted for believing that his other videos might not be satirical (and despite what he says a few them at least are definitely not satirizing the anti-feminist and are for more targeted at feminists themselves)
Libel is not an easy case to win as a public figure, and there is plenty of evidence that works against Fantano.
Especially again, because Fantano's main argument in defense is that he was called alt-right and that he's not alt-right, but the article never calls him that at all.