Reality is, if you get the correct hitch, you do not "NEED" WD to tow a trailer. Nor "SHOULD" you need to have anti sway bars. Now with that said.......it might be nice to have the above bars on a trailer that you tow, but not mandatory from a state law/code reason. RV.NET weight police not with standing.
One should use or may need a WD "IF" you sink the rear end enough that you overload the RA by taking too much off the FA, and/or you remove so much wt off the FA, that steering, FEA is not working correctly. THEN, having a WD is a good thing to put the wt back on to the FA< such that you have proper steering/braking etc on the FA. Many of the pro towers, use heavier suspension trucks, such that a 600-1000 lbs hitch wt will not remove enough wt off the FA to warrant the use of a WD system.
Antisway bars should be used as an absolute last resort. Reality is, you should be able to tow any given trailer with out fishtail sway in ANY condition! One should add an AS system as a safety issue. If you add an AS to stop uncontrolled fishtail sway, if a bar breaks, comes lose in route, or someone steals them, you're SOL on the spot! So best to make sure the trailer you tow is balanced such that it will not sway in an uncontrolled side to side motion. Many ways to do this if load balance does not work. If a trailer sways from the factory, most pro's will return the trailer and tell the factory to fix the alignment or equal so it will not sway.
Marty
92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
2014 Chevy 1500 Dual cab 4x4
92 Red-e-haul 12K equipment trailer