I think each rafter cavity should be vented and well vented at that.

My thinking is that in cold weather moisture from the living space will enter the edge of each rafter and migrate inside the rafters toward the cold outside edges. The rafters must have a place for the moisture to be extracted.

Without ventilation on the outer edges the moisture level would rise in the cold outer edges of the rafters. These should have air flowing over the sides of the outer edges to dry them out.

In the a/c season the interior humidity should be low and no moisture from the interior should enter the edges of the rafters. If moisture would enter from the outside due to humidity or a roof leak, a ventilated air gap under the roof decking would be needed and should be effective in drying out the rafters.

You should Google Joseph Lstiburek building science. Lstiburek's videos are painful to sit through (in my opinion he is devoted to making a dramatic performance) but he is considered a guru  in managing moisture in highly insulated buildings. In one video he describes how hyperinsulation has been the cause of rotting of roof structure.

In particular, Lstiburek maintains that moisture moves up in buildings and will collect at the top unless there is a means of drying to the outside at the top.