Sorry, but my head spins when folks try to make some mathematical formula out of a very qualitative process. That Houston kid, eg, had no certainty until his results came in. That’s the rub. There are so many ways to blow an app to a high reach with thousands of top applicants to choose among. Your wildcard is your actual presentation in the app and supp, not the surface details. Those are just the bones, the rest fleshes you out. Or not.
I think “randomness” is the wrong word or thought. When a top college has a type they seek (more than stats, some ECs,) you either show that or not. The issue after passing that muster is how instituional needs play. Maye they need X majors, aim for geo diversity, need a tuba player or you have a strong side interest in continuing your music sideline and the music dept is interested-- all things you cannot control for, much less predict. Instead of random, I see it as “beyond your control.”
I told mine, after good matching and apps/supps, a real personality match, that their chances were now 50-50, get in or not. The final decisions were beyond their control. Rather than stats (and we never looked at Naviance,) we used the calmom approach. It worked. It could not have been predicted via numbers.