Calculus and linear algebra are a tad older than that.
> isn't relevant today as determined by the community itself?
Which community? NeurIPS/ICML/ICLR/et al.? That's only a subset of the AI community.
Also, I'm not really sure that "pure ML/DL" is even a particularly in-demand field of research expertise right now; we've been absolutely saturated with supply for at least junior phd students in that subfield for close to an academic generation by now... whereas there is now a genuine drought of folks who speak "both languages" in AI. I think these days you really need a second field in order to not be in a horrendously bleak over-saturated labor market. E.g., systems and ML? God, please yes. "Symbolic AI" tradition and ML/DL? Yup, lots going on there right now. But pure NeurIPS et al. style work? You've gotta the best in a very, very, very, very crowded room.