> Also, the Earth is the only planet in the Solar system whose outer crust is broken into plates.

There is new evidence that Mercury is also techtonically active, so the above statement is not to be taken for granted.

[]: https://www.nasa.gov/image-feature/tectonically-active-plane...

Look at the second-to-last image and count how many arrows are pointing outward from the plate boundaries as opposed to inward. Shouldn't you see an equal number of outward and inward arrows? Or is this just a poor visualization?

I think if the forces were balanced, then the plates would not be moving and storing potential energy. The revolutionary idea of Plate Tectonics was modeling the earth as a large scale dynamic system.