Something that people perhaps don't appreciate is that typical large ships like this don't even have a gearbox (which would be perhaps 95% efficient).

They use large two stroke diesel engines which can be stopped and started in reverse. They use an extra valve in the engine head to admit air for starting and have valve gear which controls the direction.

Cruise ships on the other hand have electrical house loads which are almost the same as their propulsion loads. In addition to the manoeuvrability advantages this makes diesel electric drive advantageous.

Megaship engines are so fascinating. Over 100k horse power!

https://www.youtube.com/watch?v=gXeBQrio4Uo&t=680s

I like to think of it as: 5.6 million lb-ft of torque at ~100 rpm means if you could get it up to about 5250 rpm, you'd have 5.6 million hp.