There are a lot of factors.

Nope just two. Weight and wing area. By mathematical convention an aircraft's 'weight' divided by its wing area is what "wing loading" is by definition.

For a given wing loading, the wingspan will determine if it is heavy or not.

Abject nonsense.

Intention isn't to offend per se, but the gist of your entire post makes it abundantly clear that you really haven't the faintest grasp of the subject fundamentals you're attempting to talk about.

I have heard that someone has worked out a formula for cubic area instead of area.

You know what the proverb says about not believing everything you hear. How can something which is effectively a planar surface have a "cubic" area? [:-]

I don't know the details, just remember, as the wingspan increases, the same wing loading will appear lighter to fly

If you only realised how silly the above statement actually sounds.

Here's what I suspect you're grasping at. Given a fixed chord, increasing the span must by default also effect an increase in the overall area. It follows that as wing area increases, for a constant weight a reduction in wing loading is an arithmetical certainty.

Buy or borrow Kermode's "Mechanics of Flight". If you bother to read it, you'll come back and cringe when you read what you've written here.