The captains I asked was a captain for one of Maersk E-class vessels. They don't use the minimal amount. Unfortunately it's been a few years since I asked and I don't remember much of the details, just that the stated minimal crew is not what's on a vessel.

If a ship has no people, it also needs no bridge, control room, bedrooms, kitchen etc. If it has none of that, it needs to water system, toilets, lighting, heating etc.

And with all that gone, you could fit a lot more cargo on the same size boat.

Can you express "a lot" as a percentage of existing capacity? Because it seems like, relative to the amount of cargo space these ships already have, that percentage would be pretty small.

By eyeballing an Emma Maersk diagram, I think you could get three more stacks of containers, for ~5% more capacity.

Related question: if they wanted 5% more capacity in the Emma Maersk, what kept them from just building it that way? Are the sizes of these ships a fuel and utilization efficiency optimization problem?