To the OP:
I personally think you are making a false dichotomy between pure math and applied math, especially when you are thinking about what would be better specifically for AI/ML.
It is important to keep in mind that pure math is a discipline that primarily focuses on development of mathematical knowledge for its own sake, building on proofs and logical consequences from existing areas of math and building new knowledge based on these foundations. Applied math is essentially using the tools of math (in various fields) to apply to existing problems in the "real world", whether that is the physical world or the "digital world".
There are clearly areas within applied math that applies directly to AI/ML (e.g. optimization, differential equations/dynamical systems, statistics, control theory, etc.). At the same time, there has been much research in areas traditionally associated with pure math such as harmonic analysis, algebraic topology, random matrix theory, etc. that have found new applications in problems related to AI/ML.
I think the key is to build a solid mathematical foundation in your education, which you can then leverage to be able to apply to various intellectual areas.