Author doesn't argue against the idea of choosing a new notation, he makes very detailed arguments about why this specific new notation is clumsy to work with.
Yes but my point is that their argument is undermined by the extreme clumsiness of standard mathematical physics notation. I don't believe GA is the best possible notation for physics but it could be a stepping stone. We need more people who explore such things rather than more people who call each other crackpots.
Author is not calling them crackpots, and _is_ strongly advocating for some of their new notation, and explicitly encouraging readers to find better notation where he dnsagrees with theirs.