Sorry to necro this, but again, you see the new & existing development (Grand Mayfair etc) is currently asymmetric and lopsided: all access must be done via the current `=primary` and `oneway=yes` section. It's obvious both roads have different importance / significance.

But, your point is not without merit. A few years later when the (4? or perhaps more?) residential sites are up and running, then Tung Wui Road will have very strong argument to be `=secondary` by virtue of being "urban lateral". Right now being "rural lateral" just doesn't hit it.