It's ironic that they cite Millers work, but don't address the main conclusions from that work, i.e. that optical computing is horribly inefficient. Photons are bosons and therefore are very reluctant to interact, essentially requiring nonlinearities. The issue with nonlinearities is that they fundamentally require comparatively high optical intensities.
The authors mainly address the issue of integration density (which is also an issue), but not in sufficient detail the problem of efficiency. They handwavy this away by referring to 2d materials, but 2d are not a pancea. It's true that they exhibit very strong nonlinear coefficients (although I'm unsure if even that would be sufficient to overcome the efficiency challenges), however the overlap between the optical field and the 2d material is fundamentally very small (a single sheet of 2d material in the plane of propagation), so the observed enhancements have been very modest.
The authors mainly address the issue of integration density (which is also an issue), but not in sufficient detail the problem of efficiency. They handwavy this away by referring to 2d materials, but 2d are not a pancea. It's true that they exhibit very strong nonlinear coefficients (although I'm unsure if even that would be sufficient to overcome the efficiency challenges), however the overlap between the optical field and the 2d material is fundamentally very small (a single sheet of 2d material in the plane of propagation), so the observed enhancements have been very modest.