Work ethic and savvy.
Imo, it’s not code for won’t be successful. It’s part of the extra many colleges seek, to begin with. Vision, persistence, resilience. It may be the kid who lives rural, but finds the right local (ish) opps, rather than make excuses. The kids who overcome challenges throughout high school, not just ask on CCif they can explain their lesser grades. The LoR that reflects the continued work a kid puts in toward higher goals than an A or A+. And more.
Ime, no fixed algorithms in holistic. And “predicting” success is not about post college, to the degree so many think. Pick the right kids for your UG and they will continue to be successful after, however the grads define that. Nor ar they focused on college gpa. You can see more of how a kid might contribute on campus and in the local community by what he’s done in hs, how she chooses to write and on what.
Yes, they need to read the apps/supps. It’s only the rack-and-stacks that just look at stats.