Conversely, without the 80% the 20% might be unencumbered.

Imagine 2 Earths : one with 10 million researchers and the other with 2 million, but the latter is so cut-throat that the 2 million are Science Spartans.

And more specifically, if you knew which science to fund ahead of time we'd never have anything but 100% successes, science is often random and huge parts of it are not obviously useful ahead of time, some of which later becomes enormously useful.