I must say that I completely disagree with almost your entire post. First, you rely entirely too much on logic. It's your cognitive bias and you don't seem to understand the limitations of it. With respect to getting to the "core" of things - INTJs are all about the core issues. They constantly search for them. It's what they do. Understand the largest possible big picture, distilling a large number of data points about it and then generate insights based on that. I have absolutely no idea how you can justify such nonsense - bad job on core issues? It's laughable.
From a practical standpoint, I work with a lot of INTPs and find that they bring a perspective that I do not. They can be more flexible in their thinking than I am on the fly. They can be more facilitative. They bring up important things to consider and options. Are they as effective as getting to the heart of the matter and making a choice on actions? Generally no. I don't see it so often because they have such a difficult time making up their minds. It also can be frustrating because I feel like sometimes they are not actively listening. That is, they don't acknowledge the points of others who are communicating.
INTJs tend to shift the discussion to whether or not the right question is being asked or problem being addressed. Maybe it is and maybe it isn't. Most times, it seems not and they can help guide the discussion to a result that is more effective. INTPs can do extremely well getting people to feel like they are part of a process but the end results are often not as good as they could be because they are more focused on process rather than product.