True but your not understanding the big picture, there is a huge difference in reliability and velocity when you get to 10 inch and shorter. They can all be tuned to run but you need to know what your doing and how to balance the gas system properly. A quality factory short rifle will be tuned correctly but when the average Joe takes their 16 inch and swaps out the barrel for a 10.5 inch or shorter they usually have problems and end up changing buffers, springs and sometimes bolt carriers to deal with the shorter dwell time.
The velocity drop below 11 inch is also pretty steep per inch while 18 inch to 11 inch doesn't have as steep of a drop. Something about the 223/5.56 round needs at least 11 inches of barrel to make decent velocity. which is probably more what TDC was talking about.
When it comes to AR's do worry about what TDC says, he knows what he's talking about. He doesn't always word it well and usually gets carried away bashing bullpups but he knows AR's.
