Turns out the MarketPlaceRules.dll found in /Users/<user>/Library/Application Support/Epic/UnrealEngine/Intermediate/Build/BuildRules isn’t actually rsynced across as I previously stated. It must have been left behind after a previous local installation of UE on the Mac.
If you don’t have a copy on your Mac you can transfer the file from your Windows machine as mentioned here: MarketplaceRules.dll does not exist - #25 by ali.quaker