Mnou The MAC randomization in the regular GrapheneOS network settings is a supported feature that is expected to work for all users.
In the other direction, developer options are expected to be used by developers, on devices that don't contain production (private) data. Developer options often don't work quite right (when they work right, Google tends to release them as regular options). Sometimes developer options make apparently-unrelated parts of the system function erratically. Just a few days ago a user found that enabling a specific developer option triggered a bug in the lock-screen code!
So the short answer is that the developer-mode MAC-randomization option is for developers, for devices without private data, and does something that probably isn't exactly fit for use by users in general. It is expected that developers wanting to know exactly what one of the developer-mode options does will read the source code for the details.