Containers seem to take >=7 days from Germany's closest international port to Newark, NJ (practically NYC), last time I looked at routes and prices.

Oh, that's probably true. They're optimized for throughput rather than speed.

Ocean liners that carry passengers take 4-5

Actually, to a large extend it's fuel prices that cause these "low" speeds. Many cargo ships can be a lot faster if they have a reason that's worth the massive increase in fuel usage.

That also makes a ton of sense.