Jack, the 99S has 335 swingweight. Swingweight is a measure of how much mass is distributed to the head of the racquet. The 99S has more mass in the head than 90% of racquets on the market today. Adding mass to the handle of such a racquet does not reduce "punch"; the mass in the head is still there after adding mass to the handle. Regarding balance being a tricky thing, I agree, but with Wilson's trap door it's very easy to stash 10 grams or so in the buttcap and then remove it if it's not to one's taste.
I thought TW had the swingweight at 330? Anyway, I was referring to the static weight as "light". But you'r right, if you want it to feel more headlite than add some weight to the handle. I tried tailweighting some racquets that felt too headheavy to me and adding 5 or 10 g's to the handle just made the overall swingweight feel higher to me. Personal preference I guess.