In my experience hanmi is often taught with feet wide apart:
And some teachers emphasize an a even deeper stance like shown here.
I know one teacher who likes having his feet "close together" in hanmi and just relaxes his knees instead of "going deep".
Does this so called "stance of heaven (and earth)" relate to things thought or taught concerning IS?
Well, you could consider it as a rough 'foot in door' exercise, using the bones of the skeleton to route forces into / from the floor (ideally). Though it may be a bad one.
The issue arises if you become dependent on the back leg brace (because it feels strong). Makes it difficult to take the next step(s). The goal would be to show the kind of stability a back leg brace gives you without using a backleg brace...then begin moving with same.