Electric bikes have started off with the hub-drive designs (where the motor is positioned in the rear wheel) as the motor was meant to only assist the rider's pedalling. This concept still works well, for classic road pedelecs, with weak and light motors of 250 - 500W of power assistance. Performance off-road e-bikes, however, are another matter. Having a heavier, powerful motor placed in the rear wheel presents a serious disadvantage and drastically downgrades its over-all riding performance.
In practice it means that the hub-drive bike's rear wheel does not follow the trail's surface, but bunces off on holes and bumps, due to its heavy weight's rebound. It is like comparing a hardtail bicycle (a bicycle without the rear suspension) to a downhill bike with a great rear suspension.
Mid-drive e-bikes on the other hand, have a much more balanced weight distribution and so minimal unsprung mass. This results in a much better riding stability and manoeuvrability. There is also much less stress on the rear wheel, which means less rim damage and tyre punctures.
Mid-drive bike's advantages:
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Minimal unsprung mass;
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Better riding stability;
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Better manoeuvrability;
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Less impact on rear wheel (rim);
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Simpler rear tyre change;