Yup, this one is substantially bigger than OEM. We had a couple of patterns, and the big one was built first to see what happens. It can easily be scaled down. The other pattern is about 6" shorter than this. It could be made to any size, including OEM if someone wanted to measure it out for me.
You are correct, it will pivot around the ladder mount. However, that is where most of the load is carried. Similar as to when you stand on the ladder. The force is on the pin, then the brackets and bolts into and away from the hull. This design is similar to the ladder in force when standing close to the boat, then a compression force as you move towards the rear. Anyhow, the weight is carried mostly on the pins, with the clocking (or rotation around the pins) being controlled by the side rails as an almost horizontal shear force away from the boat. If the weight is on the sides of the platform, the side rails will be under more vertical forces as well which is actually more concerning to me than the center structure, as my current lengths will create a slightly longer lever.
The center structure is likely to be much stronger than the OEM option. The OEM platform isn't supported near the hull, and is a single vertical plate as you know. It does however have a larger plate against the hull that better distributes the compression force I mentioned. I may ended up with a larger plate that bolts right back into the ladder mount holes if it ends up being a worry after testing. I'd like to know if the hull is reinforced differently on the LX and AR, as my LS is only reinforced at the step mounts. I'd rather keep my plates there then going to the oem style with a backing plate on the thinner section.
All the forces could be calculated for piece of mind if we wanted to turn it into a real deal kit.
As far as what length will drag the water, that's the fun in testing!