You are somewhat right that the basic principle applies in general, as you combine pieces together or break a composite system apart you are always dealing with

You are somewhat right that the basic principle applies in general, as you combine pieces together or break a composite system apart you are always dealing with some form of binding energy, whether it is gravitational, electromagnetic or nuclear. But what makes all the difference are the forces involved - chemical reactions mainly involve the electromagnetic force, fission and fusion mainly involves the strong nuclear force. This is all well understood and the properties of the involved force dictate the length and energy scales of the phenomena.