I'm not sure that the ability to have original thoughts is at all closely connected to the ability to think rationally. What makes you reach that conclusion?

Unfortunately there's a second observation - there's no reason to believe such people existed only in the past, or would have aversion to blogging - so if super-smart people exist, it's fairly certain that some blogs of such people exist. And if such blogs existed, I would expect to have found a few by now.

Have you tried looking at Terence Tao's blog? I think he fits your model, but it may be that many of his posts will be too technical for a non-mathematician. I'm not sure in general if blogging is a good medium for actually finding this sort of thing. It is easy to see if a blogger isn't very smart. it isn't clear to me that it is a medium that allows one to easily tell if someone is very smart.