It is about degree. A stupid person does simply not have the intelligence to create a complex system. Those who created Multics were not stupid. But they are all forgotten now because Ken Thompson and Dennis Richie had the brilliance to come up with Unix instead.

When RISC CPUs first got proposed and designed the highly intelligent and experienced industry insiders who made the leading CPUs of the day rejected the idea.

Then a bunch of students, obviously not stupid, but not the most talented ones created the first RISC CPU blowing everybody out of the water. A design so simple even CPU architecture students could make it in short time.

The establishment of designers with years of experience was beaten. Simplicity beat complexity. And a whole industry of talented people had failed to see what was coming.

Brilliant people are wrong and fail to see possibilities all the time. They are not infallible. One of the greatest minds who have ever lived John von Neumann was outraged when he saw students develop the first assemblers and compilers. In his mind turning high level code into machine code was trivial clerical work anybody could do. No need for software to do it. His own razor sharp intellect blinded him to the profound importance of software performing automated compilation.