Current flow in circuits and nature
Current absolutely can flow through the ground, and this is something you need to believe because it has safety implications: if you touch a single live wire while being electrically connected to ground, through your feet or other hand or water, it can be fatal.

There are non-dangerous uses of this phenomenon: Single wire earth return. The ground circuit used by domestic appliances does function as a "loop" when current is flowing in it, although this is less efficient than having a dedicated neutral wire.

I think the distinction you're looking for is between "current flow" and "static discharge"; lightning and charged balloons etc are the second sort. A separation of charges is built up, then a pulse of current flows as the electrons move towards the positive charge. At the end of this (fast) process, there is no more charge separation.

In normal current flow the quantity of electrons in the loop remains basically constant. In systems driven by a generator or transformer, the electrons are moved around by the moving magnetic field acting on the part of the circuit inside a coil. In systems driven by a battery, for every electron released from the negative terminal another electron is captured at the positive terminal to maintain equilibrium.