I'm comparing a 3 point to the use of a lap AND shoulder belt in a first gen (not just a lap). In this case, both types of belts are restraining your upper body.

I see your point about not having a retractable...a user may have it so loose to give movement that it doesn't work properly. That's why in my original post I asked how snug the belts should be (I personally keep it pretty snug, with just minimal space).