It is in fact as if confidence has become a negative signal of competence. (Alternative explanation to Dunning Krueger: Perhaps this is due to Berkson's paradox. Publish someone who sounds confident or demonstrates competence. Now everyone who is published is either confident or competent, regardless of those things originally being unrelated.)
In my personal dealings, I've found it to be ever true. People who argue some position forcefully tend to crack when questioned closely and tend to try with an extra dose of bluster. People who just dipped their toes in the argument seem to know a lot but the complexity of explaining just about anything makes it impossible to construct a pithy reply.
It is also true that there is no inhibition at all in exploiting people's cognitive bias towards confidence. That is in fact how the consulting industry works. Internal people have worked on a problem for long enough to express doubt. External consultants can show up at a meeting and go "yeah we can do it" convincingly.
It is also the case that fake-it-till-you-make-it is seen as legitimate. Pretend to have a blood testing kit that works, use that to gather up investment and allies. Use the money somehow to actually build it. If this strategy had worked, nobody would be complaining.
And regarding CEOs and leaders, they are actors and they are paid as such. If you were wondering why CEOs get paid crazy amounts of money, it's because only a few people can carry off pretending to run a huge business. Plenty of people can actually do it, few can act like they can do it. You have to stay in character for years.
I've often thought that leaders are paid not just for the skills, a lot of people can do that, its the relentlessness, every day, every hour, having to be "the guy", not many can do that, or even want to do that. You have to be bent in a particular way.