On-deck cargo ships are not as common as you think they are. I mean sure, they're everwhere, but they're also VASTLY outnumbered by the amount of roll on/roll off ships. While they are for utterly massive ones, those massive ships are forced to dock at massive ports that have the infrastructure pre-built. Most of the world doesn't have those massive ports or they have smaller ports that are closer. There are a massive amount of cargo ships that are instead a 'roll on/roll off' type, similar to a ferry. That's what this ship is. The minimalistic design is odd but likely has far less to do with aerodynamics as it does with structural integrity and the fact that it's a cargo ship. It's also a concept image so any visual design could be left until the final stages, provided it doesn't impact hull integrity. It doesn't need a bunch of random designs on the outside. All other cargo ships are done in a streamlined fashion. The length of this cargo ship is actually 200m and the length of the sails are 40 meters. They're also sails and not wind turbine blades, are retractable, turn 360 degrees, tilt and designed to be retroactively attached to multiple other ships.

Source.

Seems pretty practical to me. It's almost like the people who designed it knew what they were doing.

This trend of looking at something, making wild assumptions based off of no data, and then judging based off of those assumptions without ever even attempting to verify them? This really needs to stop.

if it’s a sailboat the wind will be behind them.

Sailboats are fastest when sailing across the wind, called a "Beam Reach"

Like the other person said this is a roll-on-roll-off cargo boat meaning it transports automobiles and cargo trailers. But I believe this specific one only does new cars.

As far as being aerodynamic, on a normal boat having things like biminis up can make docking difficult but with sail boats in general, a draggy top can hurt upwind performance. Meaning if you have some sleek aero superstructure then you might be able to sail 30° from the wind, but a bunch of biminis, a big square pilot house, etc might push you to 45° from the wind.

As an example, this boat might do 45° from the wind and exposed containers might push it to 55°, but that's still better than a lot of old ships which had terrible up wind performance.

There is a different one that's a retrofitted container ship with smaller sails. They do take up the space of a few containers but not many as far as I remember.

Edit: also every spec in this is just an example.

This looks like it might be a roll-on/roll-off cargo ship, which have covers like that. But at the speeds a ship travels aerodynamic drag is minimal so you’re right about that.

And those sails will make going under bridges pretty hairy unless they can be stowed somehow.