It's actually incredibly common. Anyone that's been on the business side of a business doesn't think that way, and most engineering people don't think that way, but people that don't work hands-on with the grimy, mucky, slogging reality of business believe in the myth of a great idea.
Ideas without execution = nothing. Execution of even a mildly valuable idea = quite valuable. Most of the people I know who built large fortunes didn't invent something new or crazy. Lots of real estate and development, turning one space in the world into a more valuable space. One gentleman I know buys properties in high rent areas that are normally not profitable, and converts them into vacation/short term rental properties for businessmen staying in town who want a more "homey" place. So he's able to turn traditionally cashflow-neutral or negative properties into profitable ones with a just a bit of added active management and marketing.
Brilliant idea? Meh, not so much. Great execution.
There's lots more. I have one acquaintance who is investing and working on various technologies for spaceflight, so maybe he'll do some breakthrough crazy stuff later, but most of the wealthy people I know don't do anything so flashy or remarkable. It's just all execution of ages old ideas, like buy a space and renovate it into a nicer, more valuable space. Provide a service lots of people use for cheaper. Provide a higher quality service that is currently well used that people are dissatisfied with. Make people's lives more convenient, happy, or healthy. These aren't such new ideas. If I had to guess the ratio of a person that goes self made to holding more than $5 million in assets, I'd guess 95 to 98% old ideas with great execution, 2 to 5% new ideas. We lose sight of that in technology because we keep hearing about the new cool hotness, but most fortunes are built by fixing something in the world that you're using and aren't happy about the quality of. Hence, almost all execution, not so much having great ideas.