Poor statistical/Linear Algebra foundation

Often you hear people saying that understanding the inner workings of models and algorithms is irrelevant and a waste of time. I am currently a MS student and struggle to understand some of the inner workings of things such as M-estimation for robust regression and I believe it’s due to my poor statical background (CS undergrad).

Should I put the time into going back and getting proper statistical credentials (I want to frankly) or is it a nice to have …

algebra algorithms datascience foundation linear linear algebra people regression statistical understanding waste