I think there are plenty of anecdotes to "prove" that our F-150 trucks, when properly configured will tow large, relatively heavy, fivers, and do so with a reasonable degree of safety. I am driving 2nd F150 and my 4th F-series. My most seriously prepped tow vehicle was a 2000 F350 SuperDuty (which I sold recently, just short of 200K miles). None of the other vehicles could tow like that F350. The low end 'grunt', the ablity to maintain highway speeds in the mountains, and flatland cruising was excellent. I did upgrade to larger brakes, and added a Banks package to the 7.3L.
My point is that our F150 are great tow vehicles, for moderate loads, but if you are going to tow large 5ers, heavy trailers, don't put all your trust in your F150.
Happy Trails and Safe Towing to All Y'all..