You're correct that this ball is rated at 7,500 pounds. Keep in mind that this ball is only for pulling the trailer for my normal lighter loads... 5k to 6k GTW. If I am approaching the maximum trailer capacity, I'll probably borrow my equalizer hitch back from my dad anyway. I'll want the extra stability that the equalizer gives me.
Additionally, 7,500 pounds is right at the capacity of this trailer. I have two 3,500 pound axles. As for the ball mount, any markings are long gone, but it has a solid shaft (not a hollow tube). It's very heavy duty. I have no concerns about the ball mount.