There's a simple way to cut the BS; tell the "ace" at the dealership to show you the specification from H-D in writing. And if he can't find it, invite him to call the Tech hotline at H-D, with you sitting next to him listening in, and have them give him the spec if they can. Assuming your guy and the tech line guys can't come up with the official performance specifications, then have the "ace" pull another bike in that's equipped with heated grips and park it next to yours, then set both to max heat and measure the temps. If all else fails, file a complaint with H-D customer disservice.
It's a real shame that so many people in Harley shops seem to think it's perfectly fine to make up chit as they go, versus taking the time to get the facts. Of course, when the mother ship sets the example by doing the same sort of thing, I guess it's not surprising when the peons follow their lead.
And BTW, when the bike is out of warranty do yourself a favor and don't pay for more of the same crap from H-D. There are other alternatives from the aftermarket for heated grips that work better and last longer. Rewarding H-D for supplying crap by purchasing another set from them after your warranty expires is something only a masochist should consider.
Jerry