The point is that the robots can build things that would otherwise be too time consuming to build, on site, with higher precision than previously possible, and

The point is that the robots can build things that would otherwise be too time consuming to build, on site, with higher precision than previously possible, and with a feedback mechanism that can adapt to the environment. So yeah, surely the robot can build a rectangular rebar structure. But, it can also make other shapes which could be structurally interesting in addition to aesthetic.