JIMHO, I think your choice of barrel, optic, rail, and buttstock will have a greater influence on whether it is relatively light, lightweight, exceptionally lightweight, or ridiculously lightweight.
Usually Op Rods are solid rods, as compared to the gas tube, which is a tube, hollow. So, Op Rods will weigh a few more ounces than a hollow tube. There are low profile piston gas blocks, so weight-wise, those are on par with a run-of-the-mill DI lo-pro GB.
like I said, just MHO.