It's not about race, it's about culture and education. For instance, Chinese immigrants are usually an economic boost anywhere they go, due to the can-do attitude and respect for education and business activity in the Chinese culture in general.
Also the Chinese immigrants in question, like many others, usually immigrate seeking a better life, it's a strong self-selection filter. Middle Eastern immigrants of last 10-15 years in Europe are refugees, displaced by wars; they did not choose Denmark (or other Western European countries) because they planned to integrate and to prosper there, they ran there to merely stay alive. They need a lot of help adapting. Even if they are very willing to work, they may lack the knowledge required for gainful employment, and there are only so many dish-washing and trash-disposal jobs.
Those who adapt can make it big; consider people like Freddie Mercury or Nassim Taleb.