I am not sure what your "take" on the Steel gamemode is exactly, but I think it would be worth defining so that you can better figure out what you're trying to do with the map. Is it like more modern takes (Outflow for example) where the final point only really becomes a viable capture once all the other points are capped? Or is it like Steel / Reactor where the final second to last point is about as equally capturable as final?
From there, I think you should try and design each point to play as an isolated / compartmentalized piece, and think of each as its own A/D point. Steel manages this by making A and B points that are equidistant from both red and blue spawn, and C being a straight push from B with red spawn jumping back to compensate for blue's walk distance.
I think you've got a dynamic that works for A and B, but the walk distances don't quite work for C or D. In addition, if blue team decides to ignore A and push B / D at the start, they can gain way too much ground. Steel blocks C off entirely for blue team until B is capped, and there is little ground for them to "infest" on the way to E.
I think your map also just suffers from meta, because it seems to be a guarantee in tests that blue WILL try to set up a nest for attacking D. D has proven itself semi-viable to storm since the red rotation times are so long, so it bleeds more blue players from the A offense, and really just stifles the dynamic of the whole map. On Steel, players don't really seem to try this much because A is a fairly difficult push and because E simply does not feel viable as anything but a distraction.
In conclusion: I think you need to restructure/rescale the map in a way that reduces walk times in general across pretty much the entire map. Both teams need to be able to rotate between their options quicker, and the final push to D once all points are capped is simply oversized and does not work. I think you may need to design A and B in a way that is scaled more akin to Steel in order to do this, as they are the main rotation "branches" once the map has moved onto attacking C and D, and therefore extend all walk times. (Alternatively, give blue a forward spawn?)