OP: "Out of the approximate 35k people that apply to Harvard every year, how many of them do you think have the scores, grades, and ECs needed to be even considered?"
I'd speculate the number is a lot less than most people thought (probably much less than half of the commonly believed 80-85% of the pool - many of them can handle the workload if admitted, indeed, but won't stand a real chance - these are two quite different things although many may not realize it), due (but not limited) to the following reasons:
1. Although the applicant pool has been growing significantly in the recent years, the number of "really competitive (not just qualified) candidates" among the senior classes nationwide doesn’t change significantly year after year;
2. Just opposite to what many would have thought, a deferral or even rejection from the big H (or YPS) is not really that heartbreaking - as a matter of fact, it's a lot less painful than that would have been caused by a rejection from a "more reachable" or "good match" college - everyone knows it's extremely hard to get in, so it is "normal", "understandable", and “OK” to not get in; and
3. Of course, the fussy "holistic" process itself and the seemingly “easy” requirements in H's supplementary form (compared to other highly selective colleges) have also produced a lot of false optimism and the "lottery-bidder" thought (nothing to lose except the $75 fee - so why not give it a try?) among way too many students and their parents...