Free Speech and Academic Freedom are two separate things. The first is a legal concept and the second, while there may be laws in some places, it is usually more of a contractual matter.
I can't comment on the relative balance between Europe and the US (or other places), but the purposes of the two are quite distinct, philosophically. The first is a political matter, encouraging a robust "marketplace" of ideas in which, hopefully, the best ideas come to the fore and drive policy, while still permitting dissent. This is, or should be, the right of every person, regardless of their political system. Sadly it is not universally recognized.
Academic Freedom, on the other hand, is intended to permit certain academics to pursue ideas, even unpopular ones, in a research and teaching context without (much) interference from authorities. But the "authorities" are usually those within the academy, not the wider public. It is therefore supposed to permit the development of ideas, rather than just their dissemination. There may not be a lot of controversy about most mathematics, but there is in the world of philosophy, social science, and other, more human, domains. There are some people who would much rather that some ideas not be developed or even considered. Academic freedom works in this space, if imperfectly.
However, there are abuses of both. The reference article on academic freedom notes a few of the cases in which academic freedom protected statements that were not really germane to the research of the speaker. Both William Shockley and R. L. Moore were noted racists who were permitted to continue work while espousing some pretty evil ideas. But part of that was just that their professional work was exceptional and people didn't want to interfere with it.
But the opposite thing has also happened. The mathematician Ed Dubinsky was fired from a tenured slot at Tulane (about 1969) for speaking out against the Vietnam War. It caused a stink in the wider mathematical circles and he had a lot of help to continue his career. That was a free speech issue, however, but tenure and academic freedom didn't provide any protection whatever.
The world is messy. Protections are imperfect.