except for: you can still get that stretching effect when you run a naked cable with no housing anywhere, as with a cable run from a DT shifter to a FD...maybe the housing compression adds to it, but if the housing stopped compressing after its "break-in" then none of our adjusting barrels would work.
Zinc doesn't rust, true, it corrodes to chalky gray , but I have seen dozens (hundreds!) of plain steel cables that started out galvanized, lost their zinc, and then rusted...zinc is "fugitive".
Lastly: a light bodied lube is recommended for unlined housing (without a teflon liner), but not grease...why? because grease can actually impede the sliding of a long light cable in a long housing (that's what the engineers say) it can increase friction, the opposite of what you desire. This doesn't apply to heavier cables that are subject to much greater loading (such as automotive clutch cables and parking brakes) those are happy with grease.