Yeah it's not a solution to everything. I imagine the standard "super light" robo taxi as a two seater with the seats facing each other. Without a driver seat you can redesign individual transport to be narrower which improves aerodynamics.
But yeah for families or cargo transport you still need larger vehicles. Or take two. And I also imagine this to be more of a "gap filler" besides public transport or bicycles. It would really require a pretty big redesign of how we live and work to reduce our energy and resource usage to zero.