alt Hacker NewsI've never needed to load 100 PDFs at once, and honestly I don't imagine I ever will. I guess it might happen for some people, so a dedicated app would be useful for them.
For me, having a separate dedicated app isn't worth it for the benefits you mention, which to me are minor compared to having to install and manage another thing (which, to be fair, I imagine Sumatra to be a very pleasant citizen at compared to Acrobat).
Even just 10 PDFs is leaner than a similar number of bloated web pages.
Documentation particularly is a big one. Then there are books, etc.
Some web pages can still manage to be leaner than a PDF, but as another poster pointed out, a lot of modern web is pretty trash...