After chatting with some other local mappers, this isn't the first time this has happened, so I've started a new wiki page for the county. The only factor you mentioned I didn't include is traffic volumes, which I can fetch if you think they'll help your case. Please look it over and let me know what you think https://wiki.openstreetmap.org/wiki/User:Dknelson9876/Salt_Lake_County_Road_Classifications