Gear drives don't work with flat wheels, you have to have belts or elaborate movable axles to keep them pressured together.

Metal gears are also considerably difficult to make reliability. I'd be interested in a history of the gear.

I'm sure it's more about infinite lever/ratio than the teeth.

invention (n): the action of inventing something, typically a process or device.

device (n): a thing made or adapted for a particular purpose

The purpose is different.

Sure; I'm arguing that the leap necessary between wheels and gears isn't really all that huge. A gear is basically just a wheel–regardless of whether you think it's a separate invention or not it's not really that impressive as going from nothing to the wheel.

A gear is a lever which uses a wheel to apply continuous leverage - I would say using wheels as force multipliers is a considerable jump in cleverness than just using them to roll around

Gears provide mechanical advantage -- i.e. gear ratio.

So do two wheels of different sizes.