Now 2D probably fulfill the same role as those used to be
Not really, the square lamp was intended to form the fixture's light emitting surface, so not covered by anything else. One could call that a form of "sealed beam" lamp: All optic is inside of the lamp, the fixture only hold it in place and provide the power...
So no losses on any dirty reflector or cover glass, as it become the usual common place with many installations after years of use...