I think you should look for another mechanic, this one doesnt know what the harmonic balancer is there for.
If its no use, ask him why did KIA (mazda) actually put a harmonic pulley in it, why not use a solid one.
There is a reason older cars had a solid pulley, they used V belts instead of multigroove belts which transfer nearly all the torque with very very miniscule slippage unlike the V belt which would bite a little deeper into the pulley if the application was braked.
The above is the same reason most solid pulley old cars with serpentine belts had a V belt for the alternator, the charade CB37, or the Toyota 2C, or the nissan CD20. To save the crankshaft keyway from destroying itself.
Now couple this with the fact that the engine shoves out high torque at certain rpms, which can co-incide with the crankshaft harmonic itself when it flexes from each firing stroke, This pulley comes into action and swallows those vibrations - on the other end the heavy flywheel tries to smooth it but also bounces it back through the crank. If you are also applying a brake with an alternator, then you are magnifying this effect.