Toot is usually accepted as a Saxon lookout hill. They had a knack of finding long barrows for these.
I suspect Yinys Cairn is the ruined corner of a hovel or bothy. I think there's traces of lime mortar between the lower courses ! I noticed that a collection of cairns, known in the North Pennines as curricks, have been listed on the Portal as a modern stone circle. They're not modern and they don't even slightly make a circle. (Tindale Fell).

"So all chronology is up for grabs in the area, the way I see it "

It looks like that, not forgetting saxon as well! There's continuity of "significance" in its position, St.Arilda's well is not too far away - she followed the fate of all good nuns who would not yield to the local tyrant, and had her head cut off. Her birthdate is 448 ad, so with roman coins there, you need to excavate below the church to find evidence of prehistoric connections - but I bet its there.....