Having towed the same trailer (RV 21', 3600#) with my 4Runner it was ok stability wise using no WDH/Sway control. You definitely felt the strong winds you could feel it tracking the ruts back and forth on the highway. Passing vehicles made were so-so feeling.
With the WDH/Sway control it was much smoother. The cross winds were not as noticeable and the same roads felt much better. Passing trucks were much less notable too.
I don't find this chassis the best towing chassis. But my only other comparisons are a freight liner dump truck pulling bull dozers and front end loaders and my F350 Super Duty Diesel pulling a 5th wheel.
For me the extra $600 is worth the control and safety for my family. I know many people are opposed but I think everyone has to evaluate the risk for themselves.
We watched a car get pushed off the road on I-95 last year when a large travel trailer bring pulled by a pickup got hit in the crosswinds. The had to chance to do anything. It was just pushed into the median. Luckily no one was hurt.