Back to the Ops question, I do not think you can predict sway with any reasonable TV/TT combination ahead of time. However it is obvious that it is a problem for many people.
Since the day I picked it up and the dealer installed the WD hitch, my 25 ft. TT has been rock steady through wind buffs, hard stops, swerves and a few other things I would not care to do again.
There is nothing mystical here, a ½ ton F-150 4X4 and a 5000 lbs. dry weight TT; similar to dozens of other units going down the road. That is why I wonder if some TT designs simply are not as stable as others.
Maybe there are slide/bath/kitchen combinations that create more instability than others, but that is just a wild guess on my part.
I can also say my PUP always has a little fish tailing but it weighs less than 1/3 rd. of my TT. I never took the time to try to correct it.