Thanks for the article!
I didn't know what to expect from this article but it was interesting nonetheless. From my perspective, I've always thought of mathematical or statistical maturity as being able to build up a concept from scratch and not rely on formula memorization (which is somewhat incentivized in education as a shortcut). Proofs seem to take that a step further and while I have no doubt that shows mathematical maturity, it is also somewhat disconnected from the applied version of the field that is seen in industry.