The relationship is interesting. Chris is trying to find a minimal set of functions good enough to derive the rest (a worthwhile goal, and it mentions at the bottom that I did something similar in BQN). Part of my current thinking about primitives is that it's not important how many there are, more that each represents a coherent simple concept. But primitives that are too similar can cause problems for memory and maybe intuition.
It makes complete sense and I'll add the same thing to BQN if it gets complex numbers (this is why ⍳ is on the keyboard, but other options could be better).