Since the max trailer weight of the 4Runner is 5000 lbs, there is no need for a weight distribution hitch. The stock trailer hitch is more than capable of doing that.
From my towing experience with my 4R, if I had to tow 5k on a regular basis I'd buy a new tow hitch....attached to a better tow vehicle.
On the FJ Forum it was often suggested to replace the factory hitch especially if using a weight distributing hitch, how good is the stock hitch on my 2020 T4R?