Some shooters adjust adjust to different stock dimensions relatively easily. For others (me, for example) do significantly better with a gun that fits well. The "each gun is different" concept never helped me (although there is certainly a point to it).
If you find that you shoot one gun (with its specific set of stock dimensions) better than others, it is very likely that it fits you better, or is closer, than the other guns. While I wouldn't run out and get custom stocks for all the other guns, I would take thoughtful steps to move the other guns (one at a time) to those dimensions. It is quite likely that it will help you. Different weights balance points and moment of inertia won't change much, so the guns will still be different.
Take it slow after a change (a hundred rounds is minimal) because it takes time to settle in and get past the placebo effect.
