Being unable to give a good talk is quite unusual definition of smartness:) But I can see where are you coming from. Indeed that analytical type of smartness which is so useful for engineers often correlates with introversion. Which doesn't help when it comes to dealing with people, promoting self and building your position in the company.

Probably.

There are many smart people who are good talkers. But I only know them from the Internet.

The top scientists and engineers of our time. The leaders of the biggest companies are often engineers themself.

But they don't make the mass of smart people.

It seems like many managers have a network of mighty people, which just lets them float over the real world. They get fired here and a new job (as good paid manager!!) somewhere else in no time.

yup, let's replace "smart" with technically competent/proficient :)