I was mostly referring to the point in the talk where he claims that just relativity and quantum mechanics is enough to imply that there are no spins higher tha

I was mostly referring to the point in the talk where he claims that just relativity and quantum mechanics is enough to imply that there are no spins higher than 2, he kind of skips over that part. In that view I'm not convinced renormalizability is a strong enough property, since the graviton is famously non-renormalizeable (or so it seems, anyway). But I'll have a closer look at the quora thread; maybe someone has a more 'fundamental' argument.