"Great idea" is an extremely subjective thing, and I don't even mean it in a loose sense.
Many people think great ideas are things that are so obvious like flying cars or fixing cancer, fixing aging, going to mars, fixing racism, fixing global warming, etc. They are great ideas, but at the same time they are all just obvious ideas. If something is obviously a great idea and has great market potential, it would be stupid for a large company to be not working on it. That's why these ideas are mostly tackled by already large companies and almost never by startups. In fact I have never seen a startup that succeeded by working on an idea that was already obvious to the masses, nor have I seen world-changing come out of this. Most groundbreaking ideas started out as something you would think is not one of those "great ideas". Use the same Apple example, most people didn't think personal computers would change the world, they just thought it was some nerdy tech thing that would stay as a fringe culture. That's why IBM got into the game late.
That said, I am not disagreeing with you that philosophers are bad, I already mentioned that. I use the term "philosophers" loosely here. For philosophers, theorizing is execution, it's not like they can build something. And I totally appreciate thought experiments.