The new Sphere would, in Fithz Hood's example, mean -5, doing nothing wit the stockloss Militia gives.
Right?
But what would this mean after drastic changes after, for example, Lotus?
Player A, who played the lotus might have given up a considerable amount of resources to get some Tower & Wall. How you describe it, Sphere here will reduce A's Tower & Wall, but not return the stock.
Slightly too obliterating, Id say...
To name another card: Road to Valhalla.