I *always* accidentally clicked the adviser button. It was so non-descript in appearance that I always thought it was what I was looking for. I clicked on it whether I wanted to see diplomacy, or social policies : "uh non descript triangle, that must be the diplo screen right". Scumbag brain. I, for one, am glad it's gone. As others have mentioned, mostly useful for military. There should really be a better way to check that out.
My other UI pet peeve is how you can't access any of this information when a leader barges in and wants you to denounce or declare on someone else. You can't access your diplo screen from this leader-visiting-you screen, and you're supposed to just decide based on your memory of the political situation and your deals. Seems I'm never quite convinced the resource he's asking for is my last.