To answer you question, its yes and no. The 13' and 14' models, Ford did reinforce the rear frame more than the previous years. To say that solved all problems would not be accurate because if you over drive you truck, you will bend ANY frame.
What the aftermarket brought to market was the bumpstop kit. It braces between the rear frame and uses shocks to dampen the force the axle has when it come close to the frame. Without it, Ford just has two rubber foam pads on the underside of the frame. You hit that too hard, you can bend your frame (even if a 13' or 14'). Install a bumpstop kit, not so much.
Do some of your own research. There is TONS of stuff just on FRF about it. Your question really is old news.