What if instead of slowing your fleet's burn across the board deep hyperspace instead just slowed your turn rate? I think this would lessen the impact of large walls of deep hyperspace that block off constellations and generally slow travel.
It might just result in not steering at all and just flying straight, though, since the point at which you boost off storms is generally with large fleets (which are also slow, and slowed by hyperspace more) that can take the supply cost while you go around when you're a small fleet which is already otherwise fast. More specifically, it might end up punishing small fleets for going around while large fleets just fly straight to their destinations every time without fail (as they're no longer slowed by going through deep hyperspace and already boost off storms while small fleets don't currently care about deep hyperspace but do care about storms).
Just throwing an idea out there.