It turns out that someone independently made visualisations of the structure of the Stacks project.

He or she also performed some statistical analysis, but I'm not sure the metrics of how important a result is are chosen appropriately. For instance tag 07FJ appears in the top 10 list, just because it refers to so many other tags in its proof. That does not necessarily mean it is important because it heavily depends on how a statement and its proof are written: if a statement is a long list of substatements, or its proof does not contain any interesting sublemmas (at first sight) then by this metric it will become important just because it refers to many other tags. The metric confounds importance and difficulty I think. Although in this case it actually is an important result because it forms the main technical part of the proof of Popescu's theorem.

I really do like the big chord diagram showing the relationships and sizes of all the parts and chapters in the Stacks project. Go check it out!