> difference between sensational headlines and 'radicalising' YouTube recommendations really a qualitative difference (the latter of which is decidedly sinister and perverse), or just a case of machines outperforming humans?

No, the difference is that YouTube doesn't get a free pass; you don't hear “so and so was radicalized on Fox News (or OANN, or wherever)”, but that's not because it doesn't happen, instead it’ll get blamed, if anything, on groups and alternative media that the radicalized individual fell into after being radicalized by something shaped like traditional media.