Interesting. This was my son’s approach - except that it wasn’t an approach, it just happened, naturally, because he was, well, passionate about it. A very big spike in instrumental performance music. His GPA was 4.18W out of a max of 4.4W/maybe 3.6UW out of 4.0. Nowhere near first in his class at a good suburban public school. ACT 36. Had the occasional B, especially in math. Mostly highest rigor coursework. He got into Harvard EA, decided to go, and withdrew his other apps and didn’t finish Yale/YSM, and Columbia/Juilliard. I had read that the spike was the way to go - and it clearly worked.
I do not believe that these hyper-selective institutions are looking for “well-rounded” individuals, with fantastic grades, fantastic SATs, class president, editor of the paper, and captain of the X-ctry team. They have many applicants like that, so many that they could fill the class ten times over with them. I believe that they are looking for students who have excellent grades and SATs, plus unusually high achievement in some other field of interest, that implies that this person is going to achieve something outstanding in life, and reflect well on the institution.