Yeah I dont like a short barrel on a 308. 18 is about as short as I like to go. My Savage Scout is 20 and its just right.
hindsight being 20/20 I think you are correct. You need at least 18” to stabilize a .308 round. .308 is pretty picky with bullet weight and twists. I remember trying to shoot “Special Ball” in a national match rifle with a barrel made for “National Match.” The results were not very good.