There's a straightforward (if not necessarily easy) way to test this hypothesis. Go look at founders and see what fraction are engineers vs project managers vs sales/marketing/business/etc. in their previous careers. Then go look at who is successful and how their success is positively or negatively impacted by their experience.

I haven't run the numbers but I have the impression that "idea people" tend to flounder without a strong technical co-founder. In contrast, technical co-founders can make it on their own, though there may certainly be challenges in doing so. Those roles are also very different in terms of what you can hire in as early employees vs what absolutely has to be a part of the founding team.

Almost everything in a big organization is a team effort, but that doesn't mean you can't tease out the relative contributions of the different parts. And I think you're undervaluing the engineering contribution substantially.