Hm? I think that the last two elemental pairs are the most defined. You can't really find thematic and mechanical card opposites in for example Fire vs. Water, but in Entropy vs. Gravity you have Supernova vs. Black Hole and Maxwell vs. <pretty much any Gravity creature>, while in Aether vs. Time you have Twin Universe vs. Rewind and Mindgate vs. Hourglass.
My statement was rather related to the naming of the elements, not to their behaviour or implementation.
In that sense Gravity (which is something completly different than order) and Entropy are definitively not opposites, even though you might be right, that single cards of those elements reflect that quite good.
