Ran a quick test with my IJN gunners, although they're only lvl 97 ebve gunners so they're a fair bit higher than at level gunners are, spread seemed pretty decent to me.
I think if your spread feels unusably bad then your gunners either need more experts/vets, or if they're already full of experts with many vets then simply leveling them to increase the accuracy cap will probably help. Increasing the guns accuracy themselves would probably make this ship too accurate with 120 gunners.