Did some more investigating this morning and sadly I think you’re right. Found this in the order guide (thanks for the tip):
Power-Deployable Running Boards (Not available with Lariat Interior Trims 6J or 6B, SuperCab, or Sport Appearance Package (17K) (unless 17K is ordered with Tremor Off-Road Pkg (17Y))
Not sure why Ford does this. Lariat Ultimate costs $5,075 with or without the power running boards.
I have a call in to the dealer to confirm but it’s not looking promising that I’ll get what I wanted.