That's assuming top-tier engineers are a fixed percent of graduates. That's not true and has never been.

Does 5x the number of math graduates increase the number of people with ability like Terrance Tao? Or even meaningfully increase the number of top tier mathematicians? It really doesn't. Same with any other science or art. There is a human factor involved.

Suppose there's only one Terrance Tao. Then sampling from 5x the number of people increases the probability he's in the sample (by about 5x).

Suppose there's more than one. Then sampling from 5x the number of people increases the average number of him that you get (by about 5x).