Since the equipment are individually grounded, wouldn't the power supply ground be useless and not need to be connected?

The power supply ground is to ensure that the three-phase ground voltage is not higher than 220V, and can get the centerline and set up, this is the power supply grounding. And equipment grounding is to ensure personal safety settings, this is the safety grounding. Although the two can use a grounding network, but the role is different, grounding resistance requirements are also different.