Graphene is supposed to be more efficient than copper, but it probably makes more sense on a phone where the chassis is thin and is fanless. And the smaller size means less extra cost.
Now on a MBA you could say it is also thin and fanless for laptop standard, however, there are regulations dictating how hot the skin touching area is, so it is actually not the best solution to transfer heat away to a concentrated area too efficiently like the bottom side of the M chip (in fact Apple even added an insulator layer to prevent heat going downwards).
On Macs that with fan and heatpipes, especially with finned heatsinks, then graphene coating on copper for these parts can prove to help efficiency. This is where I see it can be deployed as these are usually pro tier products that charge more. Perhaps on Max models of 14" 16", and Ultra models of Studio. The M1 M2 Ultra studios already got a beefier copper heatsink than the Max variant so the same chassis can scale to a different thermal envelope without changing the rest.
