All following in the spirit of good debate.;-)
Fire your first shot from a double gun and you have upset your perfectly balanced apple cart by an ounce or so. Does that affect your lateral handling?
That "ounce or so" came from very near the balance point, so it has minimal effect on balance or swing efforts. Since vertical and lateral are the same factors, I think it fair to say handling is little effected.
Gun fit and balance is important, however have you seen the guys that can shoot a perfect score at skeet from the hip?? It's all hand eye coordination and practice.
I've seen 25's from the hip. Good gun fit reduces the need for high order hand-eye coordination and practice.
Chasing ounces is like running past dollars to pick up nickles.
What do you do when all "the dollars" have been picked up and you are still a nickle short?
DDA