So, do i get this right?

With a chance you can produce a special item at the workshop what needs a day to produce.

Ok, and with that item, you can only use it to produce another item what you can only sell at to Heo Seungwon.

That needs another 3 hours in my case. My worker produced each one of it. So i get a single

item at the end and it sells for fixed 98 mill. All of that items have the same price.

So, you set this worker up to produce 2 items what needs over 24 hours at least and

you get finally 98.000.000 Silver.

Do i miss something or is that the only reward or what you can do?

Yep, that's it.

Great.
Thats like almost 3 mill per hour. Tremendous profits.

Well, it's better than what most other workers produce.  Worker profits haven't been addressed in ages.....

If you want real AFK profit, get as much fishing mastery as you can and AFK fish at those few areas where you catch red-grade fish.

You were expecting Billions/day from 4CP of passive income?

The real money makers there are the buff items anyways, if you're smart about how  you use them

VoidSinger has a point. Royal workshop gives passive income with very little investment -> 5 CP for unlocking the workshop and 1 or 2CP for lodgings for your workers. And it's not level-, mastery- or gear-gated in any way either. Even gathering should give higher profits than the workshop, purely based on the fact that players invest actual time into the activity.