The reason the paradrop from the WTO is underpowered is by that point the units are faster by simply moving on land. To paradrop a unit must stand still for one full turn, but with roads or railroads everywhere, a unit can easily move further than a paradrop allows. Even across water, I've often found it faster to simply move close, embark, then get back on land.
In addition:
- World wonder.
- Most citystates within a short paradrop range are usually allied already.
- Near the end of the game (or past it since the UN can be built earlier).
- Diplomatic units are still capped at a finite quantity.
Considering all this, I'd suggest the WTO's bonus lets diplomatic units paradrop anywhere in the world.