I see no compelling advantages for SP artillery.
Put me in the “Towed Artillery is lighter, cheaper, faster, and more durable” column.
Then imagine that you have 8 inch howitzers firing in GS reinforcing; 203 millimeters of pure, precise devastation and 200 pounds of America's best HE and forged steel to overlay your fires.
Nice, isn't it?
Now please don't tell me that we're back to towing 8 inch howitzers...
In that kind of combat environment, the King of Battle needs rapid-moving and rapid-firing SP artillery, not just light DS.