I don't think assembly has any relevance, and the thing with CS that's relevant is almost entirely with complexity theory. This sounds fancy, but it basically boils down to recognizing O(n^2) vs O(n) vs O(n log n), which in practice can be reduced to "use the right datastructure" and "use the right query".
Frankly, I think far more performance problems nowadays lie in things like insane SVG/CSS animations for every possible loading spinner than in developers not knowing their O notations.
