It may be a lost art for game developers. Far from it for CG grad students and researchers. Quite the contrary, it's actually part of the rite of passage, heck

It may be a lost art for game developers. Far from it for CG grad students and researchers. Quite the contrary, it's actually part of the rite of passage, heck an undergrad level prerequisite to know these things like the back of your hand, plus a whole lot more, to do graduate level CG work. Even if you're not a researcher, but wish to write your own path tracing code for example, you would end up learning this. So no, not a lost art at all in my opinion.