This seems to make sense. But these disciplines, although old and established, have spread across (diffused, if you will) a larger area, such that they become umbrella terms for many other studies which may not be specifically concerned with the formulation of ideas, and even less so in a quantitative and procedural manner.
Thus it is still not entirely clear whether these older disciplines deserve credit for providing better training in representing ideas than straight-up CS.
I agree with you that the direct benefit of these disciplines is not entirely clear; must research needs to be done in this area. One thing that is clear, however, is that the undergraduate CS curriculum is not particularly good at teaching this way of thinking. The closest you can come to achieving the effect of English and Philosophy on your thinking is a well designed CS curriculum focused on theory. I've found that the students here who find theory interesting also tend to be good programmers. Again, all of these thoughts are based simply on unscientific observation, but I believe there is a provable, related truth that might come out of them.