IMO the style is about the base malt and the yeast. Simple grain bills as well. (three malt max) I do think you have to have 'some' crystal in there but not a lot. A sprinkle of RB would be fine to get the color right. Mashing at 158 and under attenuating seems to defeat the idea of eliminating the sweetness.
I don't think I ever mentioned the word "sweetness" There you go putting words in my mouth (or fingers)
. It is a common misconception that high mash temps and underattenuation will create "sweetness". The reason you mash high is to create long chain dextrins which lead to mouth feel and chewiness. Maltiness is often confused as sweetness. Melanoidin, biscuit, toasty, etc. is along the lines of being malty. The reason for using WLP001 and slightly underattenuate is to leave some of the dextrins and prevent the beer from being thin. Just because the beer may be underattenuated does not mean it will be sweet. Considering Cal Ale yeast can easily attenuate to 80%, by underpitching and keeping the ferment cool, it may only attenuate to 70-75%, which can still give a dry perception. Which is right in line with the specs given for WLP028 scottish ale yeast attenuation percentage of 70-75%. Maybe saying "underattenuate" was a poor choice of words, the goal is lower the attenuation percentage.
Lots of things besides underattenuation can give the perception of "sweetness." Alcohols, fermentation esters, crystal malts, and even some hop varietals. I have had plenty of Belgian beers and IPAs that I know are bone dry, but give the perception of sweetness because of the factors I previously mentioned. I also know for a fact that Lagunitas mashes their IPA at 160F and there is no apparent sweetness in that beer. Having brewed Jamil's recipe more than once and based on his success in competition with that beer, I would definitely say the recipe does not create a sweet beer.
In terms of a standard Scottish ale recipes there is more than one way to skin a cat. The one thing I would say is DO NOT use peat malt!