What are we debating here? If you don’t understand what Yale looks for, what they say and show, this is hypothetical to a ‘pie in the sky’ degree. How do you know what ECs would be “good,” much less great?
If you did “nothing to fatten up that resume,” what shows them you’re likely to explore a nice range of ECs in college? How does that "show “enormous promise and genuine curiosity?” It’s a mantra among some on CC to repeat, “Just be yourself.” But Yale is looking for a level of activation and depth and breadth, to show openness to new experiences. (And that doesn’t mean any old club.)
If you don’t know what matters, how do you write a “killer” essay? This is about admission, not a writing contest. Not about imagination, per se. “Passion” is no “it” factor. Other demonstrated qualities matter.
So go understand holistic, the fierce competition, and the cherry picking among top academic performers who hit the mark in all ways. Look at what Yale really wants. Without that, I don’t see how the app/supp can be effective.
“Potential” is trumped by results, academic and other. Show, not just tell.