Which smartphone, laptop or desktop does not have primarily closed source hardware and firmware? It's not clear why you made this post. There are no closed source kernel components. It's unclear where you're getting this information.
We don't understand the question you're asking about components becoming open source and how that relates to writing our own drivers. We have no plans to write our own drivers and it's way beyond the scope of the project. There's very little benefit to from doing that and we have much better ways to use very limited resources.
Pixels are gradually moving towards more open source firmware and userspace driver libraries. If we added support for a new Snapdragon device, that would all be regressed. When they move away from Tensor being based on Exynos, it will likely get significantly better again. There's no good excuse for still having around closed source libraries beyond the Mali GPU library at that point.