I want to be a fly on the wall when you tell "that little tidbit" to a Benz dealer! I'm not quite sure, but I believe your doctrine cite, deals with LKQ parts. Referred to as "Like Kind Quality". The Hellwig is much beefier, which no doubt reduces sway as reported by so many posters. But, in reducing sway it would appear the stress loads are torsionally transferred to the axle, though the links, thus reducing sway.
My guess would be if your MB suspension expierences any failure in the area that the sway bar effects, MB might raise an arguement. Only user installation and outcomes will determine that.
Oh, and as for the burden of proof relies with MB, good luck telling a dealer that one, when your MH is laid up during camping season, and your getting into finger pointing.
Until somebody runs into a problem, I say go with it.