Interesting. I don't disagree with your position on LI or others here, however, I think how you use the network is relative.
I find relevance and meaning in how my connections are related to other people. And yes, many of the people connected to other people I want to know don't really know those people... but it helps me identify a pattern and a path forward for outreach to people I want to know.... (sounds confusing, I know). 99% of the time that path leads me off LI to pursue a route to a person via a phone call or email. LinkedIn makes this discovery process pretty easy; it's a invaluable tool as I navigate a very crowded business world.