It's hard for me to understand the ratio of the relative body of work that turns out to be useful versus the relative body of work that hasn't seen application yet. Across all institutions, pure mathematics is an extremely small field; yet their papers have an (almost) infinite amount of time available to find an application.
The question that's relevant here, though, is what fraction of pure mathematics is ever useful outside pure mathematics.
I think this would be difficult to measure. My guess: only a small fraction, but some of that turns out to be incredibly useful.