Indeed. However, they are also very slow (usually around 30 km/h) and more importantly very slow to change that speed (cargo ships starts braking 5-10 km before port). All due to heavy inertia. The ships' engines aren't doing a ton of work themselves either, per unit of time.

Work per time is power in physics. A ship like this has an engine of about 100 000 horse power per google, which is about 500 cars' worth of power. And 10th of that is about 50 cars. Which matches thereabouts a huge sail in a strong wind at large altitude in the open ocean like this, I think. My back of the envelope math checks out.