I've not driven a truck-5er combination, but I do know I've driven several tow vehicles with trailers. If the truck is too small for the trailer, towing is a nightmare. With the right truck-trailer-hitch combination, towing is sweet. I think 99.99% of travel trailer towing problems is because of too much trailer for the truck. Whereas, a 5er is more forgiving with the same truck.
I do know, my current rig combination (with the integrated brake controller) is a very sweet ride! We've done several long trips now (over a thousand miles one way) with this set up, and did not have any problems, sway, scarry moments, nothing. Truck and trailer acted as one unit. No problems.
(However, i-65 through Montgomery Alabama has us down to 35 mph. BUT everyone else was running about the same speed.) That was the only place I felt I had a trailer attached.