This strikes me as overly simplistic, so say the Jordan Box isn't necessary because you already have it in "better" performances by Martinon. I have both and wouldn't be without either. Both are full of superb performances which are different. I don't find either one "better" than the other.
Again, this is a personal choice. Martinon is one of my favourite conductors and I don't recall any of the Jordan performances as being superb; some were good, others just serviceable. I posted my thoughts on the Jordan box as I worked through it and if I go back and check I may end up with egg on my face after that last comment.
One of the problems with buying large box sets of the French orchestral repertoire is duplication so for Ravel, Debussy etc Jordan is up against stiff competition. Unfortunately his set doesn't have much in the way of variety. I am sure it will give a lot of enjoyment but with the benefit of hindsight I wouldn't buy it again.