I’m not at all convinced that exterior insulation would have lower labor cost. You have to competently install sheets of rigid insulation, and then you need to competently install siding over it.

Insulating cavities needs some skilled labor if you use mineral wool, but a skilled installer goes fast. Or you can use some kind of blown in product, which takes very little labor. (I have never seen competently installed fiberglass batts. I’m not sure they really exist.)

Insulting cavities well is immensely labor intensive and unfortunately is still required in homes with exterior insulation so you're kind of getting the worst of both worlds. Exterior insulation is an absolute breeze in comparison though, there are tons of product on the market that integrate the sheathing and insulation into a single unit so it installs just like any other exterior sheathing would.

I watched a crew install a blown fiberglass product: they stapled fabric over the walls, poked holes in it, and stuck a hose in each hole so a machine in their truck could flow fiberglass into the cavity. It went very quickly and fully filled the cavities.

John Mansville Spider Plus looks like another interesting product — blown fiberglass that is just sticky enough that it can supposedly be applied to walls and even ceilings without anything to contain it.

Exterior typically requires sheathing and insulation is attached to that sheathing. Extra work is required to tape up the seams though it eliminates the plastic house wrap required in most areas in the US which is attached with staples or a nail gun.