For a device leaning into shelves to grab things, being dynamically balanced might be useful. Like a racing sailboat with a movable keel or ballast. But you could do that with a three wheeled design.

I bet there's also a static version of this bot with three wheels, slightly larger footprint, where the battery pack is situated over the third wheel for leverage.

But the swinging battery pack? In theory it reduces the footprint of the bot, but any time the bot is trying to grab a package, the battery is moving. Which means you can't let another robot or human enter that space. So either you have a very very complicated calculation of what areas of the warehouse are 'empty' at any moment, or your logistics program has to treat the robot like it's its worst-case footprint at all times. At which point you might as well make it static. Right?