Well OP, what re you gonna do? Maybe you are never going to go down a mountain?
I have had fifth wheels that always came in at + or - a smidge 10K lbs.
I towed one consistently thru the smokies and up and down I26 south of ashville. 13 years on that 7.3 diesel without any brake assist.
Experience, I got a little also running 18 wheelers from coast to coast without running and exhaust brake.
What would one expect a stealer to recommend if he is selling the product?
Also, with my experience I would say you do not need one. There again those who have all the upgrades hung on their tow vehicles would say you will not make it down the first grade.
How did you all get along with that rig in its first years?
I can see right now that you will probably not venture out without that pac brake the sales man is pushing for.
So Happy Trails and do what makes you comfortable and I apologize for all the you gotta have it advice here without really delving into driving habits and personal feelings.