I don't know what the weight capacity is, but I have seen several tailgates carrying massive spare wheels, jacks, light bars, and so on. So I do believe Ford made them strong enough to hold alot, knowing owners would add stuff.
I have the same issue in the Raptor F150. I have tried to just step on the running boards when I get in and out. I can't think of any other way to avoid "dragging your ass across the seat :) " besides stepping on the running boards.