That mental picture doesn't follow the rules though.
You can have this large sized multi 1000lb earth elemental grappled and pinned to the ground with a single hand. You are also able to move 15 feet per round while pinning this earth elemental to the ground, dragging it with you as you move. You are also able to stab this earth elemental with a rapier which has a blade that is a few feet long. Instead of suffering any penalties for attacking with such a long weapon while grappling with the elemental, you are actually making your attacks at advantage.
From a realistic standpoint, none of this actually makes any sense . It might be argued that you could pin a creature of your own size to the ground and have a hand free to punch it (if you used your legs to pin it). It is ridiculous to believe that you can pin something to the ground that takes up 4 times as much space as you while also still having one hand free, and also not utilizing your legs because you can drag it about as you please.
First explain to me how the existence of the Earth Elemental in this scenario is in anyway "realistic".

If you were running a "realistic" game, very few of your opponents would be larger than Medium. (Maybe a bull, bear, or tiger, etc.)