Secondly, there's all kinds of regulations. A container vessel is operated 24/7. If 7 is the amount of people working on it at a time, in practice the crew will be twice that.
In any case, your response lacks a lot. The person you replied to talked about big boat shipping and how it is not going to be automated any time soon. You only account for the crew on a vessel. There's the customers (loads of which still like to send a fax), lots of outdated governments, outdated vendors, other companies, etc.