999 Look at some of the Midland Demond's or gun made by Davis , Fred Williams , Ward's to name but a few. Not all English were built like Purdeys many were knocked out by guys on a pittance to be sold for a few shillings. They were cheap and nasty and fortunately most are long gone . So Engine turning was a way of making a barrel look better ,it would be cheaper to do as it was machined as opposed to the hand work in matting or file cutting.
I am not saying that it was true in all cases ,but I have seen far more cheap guns with engine turned rib than better quality ones. I have seen a lot of guns.Greener & Bonehill did engine turned ribs but this was house style and only on some of there guns .