The ballast vent on my 2000X is almost on the centerline, just 5-1/2" to the portside.
I agree that a given ballast weight is always the same in the boat, no matter how it heels, which seems your point, but weight by itself will not act as RIGHTING ballast.
That is why it is dangerous to have partial ballast. Half ballast will assume a low level in the tank, draining the high side ballast tube, due to gravity, and keep pulling straight down on the center of gravity of the boat, where its ballast weight will not help right the boat.
The only way the water ballast can help right the boat is if it is kept, or lifted, beside and then above the center of gravity, in the side tubes, its leverage acting against the bouyancy, pulling the boat back to vertical.
Another way to think of ballast .... In a fixed ballast boat, the balllast may be concentrated in the center, but of a deeper V shape hull. The ballast weight cannot shift its center of gravity, and when heeled, the ballast's center of gravity is lifted higher than its resting level, causing it to pull back down and give righting force to the boat.
Same thing in a full ballast tank on the Mac. It's center of gravity will not significantly shift when it is full. Since the boat is not deep enough to have 1400# of water under its centerline sole, the side tanks are needed to spread the ballast around in the relatively flat hull. Heeling the boat, by necessity and definition, lifts the high side ballast tube above the water level.