Being heavy on the forehand does not matter much. It is still less heavy than forehand of girraf.

When centaur is making his front part upright as shown in your figure, his center of mass will shift little backwards and little upwards compared to that of horse. He might be more stable than horse because weight of front part will be directly on the fore legs while neck and face of horse are leaning forward.

Being heavy on the forehand does not matter much. It is still less heavy than the forehand of a giraffe.

When a centaur is making his front part upright as shown in your figure, his center of mass will shift a little backwards and upwards compared to that of a horse. He might be more stable than a horse because the weight of the front part will be directly on the forelegs while the neck and face of a horse are leaning forward.