Multi-tasking bad for brain and makes for less effective employees

I've had a hypothesis for years after reading a similar article to this one (see link) a few years back.  The hypothesis is that many adults who either are diagnosed or self diagnose themselves with Attention Deficit Disorder don't have a disorder - they simply have to multi-task too much in their jobs or they don't have to, but they do.  Think about how much better you perform and how many fewer errors you make when you are  have the time, focus, and lack of distractions and competing demands to work on one important project.  Baseball players aren't expected to hit and field at the same time, basketball players don't have to play offense and defense at the same time, etc.   Multi-tasking continues to be shown to be harmful to the human brain and there is a known correlation between how much workers multi-task and how ineffective and error-prone they are when performing their work.

See this article

http://www.news.com.au/business/worklife/multi-tasking-is-bad-for-the-brain-and-makes-you-a-worse-worker-experts-say/story-e6frfm9r-1226625939738