but this article is explaining that unless you are selling short in the morning and covering at night, there are mostly negative returns for intraday trading, i.e. "pil(ing) in in the morning, and exit(ing) in the afternoon".

There are lots of firms and funds and floors that never hold overnight, but this research demonstrates that that is basically a statistically losing strategy. If you follow markets it's almost impossible to not notice that almost all the real action happens after hours, and the day's trading tends to "erase" whatever happened overnight. Bruce's research is hard to contradict, unless the data is wrong or his formulae or off.