I have a 2004, and have never experienced a bucking problem with it, nor hesitation that is atypical for a 4 cylinder vehicle.
Competent technicians don't diagnose intermittent problems by guessing a theory and checking to see if it's true. They use gauges and test equipment to systematically determine if each system is working properly.
Hesitation and bucking can be caused by anything that would cause an disruption of fuel, air, or spark. If the engine is in otherwise good condition (compression test and plug inspection) that could include things such as:
Dirty air filter.
Restricted fuel line /fuel filter.
Water in gas tank.
Sediment in gas tank.
Bad gas.
Fouled spark plugs.
Damaged gas cap.
Loose vacuum line.
Restricted gas tank air inlet.
Loose connection to fuel pump/ worn fuel pump.
Sticking fuel injectors.
Loose connection to spark plugs.
Intermittent short, overloaded or marginal primary electrical system.
Flaky emissions computer.
Bad aftermarket "performance" chip.
The first half-dozen are simple to check and would be things I'd check if I bought a 6 year old car, but I wouldn't have bought a used car with obvious performance problems, not even an Element.