I tape the outside, but I don't use anything as heavy as your 9oz tape.

I cut strips diagonally from glass cloth. On my sea kayaks that means I have 4oz tape on the outside and the racing kayaks have 3oz.

Cutting the strips diagonally stops the edges fraying.

I suspect you would have created a stronger join about the same weight if you had used lighter tape on both sides. Having glass on both sides of the timber makes a huge difference.

There are better ways to save weight than significantly weakening the join.