When Paul Graham uses a phrase like "great work" I can't help but only consider it as being synonymous to "work that generates a big return for the investor" in his context of Y Combinator
That probably is what it means and I think there's still value in the analysis.
What do you want it to be synonymous to? The people who've managed to do great work without generating large investment returns not that large. Compared to the number of ambitious people presently looking for advice it is small.