Loved this argument as well.

With respect to more mature research fields the entry point to ML is much lower.

Hence I always recommended people to have major in Physics, Chemistry, Biology etc but look for projects in these fields that could benefit in ML (I have a number of them about Physics).

So that argument was not novel.

But the fact that pure ML PhDs will have significantly lower multidisciplinary knowledge is a good one. It could be compensated by the fact that ML is growing fast and all kinds of people join the ride, but still.