Why slow thawing is the best way to defrost a chicken flavor wise?
I took a look at Belni, H. (2015) Consumer Attitudes Toward Storing and Thawing Chicken and Effects of the Common Thawing Practices on Some Quality Characteristics of Frozen Chicken in the Asian-Austrailasian Journal of Animal Sciences. In the literature review, the paper states that 


  ...the effects of the freezing and thawing on the quality of the meats continue to be a significant problem due to the complex physical, chemical, and biochemical changes during the processes including melting of ice crystals, relaxation of lipids, and relaxation/ proteolysis of proteins.


The author points out that, since the water fraction of the meat is the main issue, freezing rate and the formation of small ice crystals is desirable.  However,  consumers have little opportunity to control this variable, as we are using chicken that has already been frozen, or a home freezer that really doesn't freeze all that quickly.

The author examined 5 thawing methods:


in a refrigerator
on counter at room temperature
in warm water
under tap water
in a microwave


The objective of this study was to determine the effects of the most common thawing practices used by the consumers at home on some of the quality characteristics of chicken meat.

Quality was identified with regard to:


color
pH
drip loss
cooking loss (Cooking loss and drip loss are really about moisture loss * calculated by weight difference)
texture


The author found 


  although there were significant differences among the thawing treatments for drip loss and cooking loss values, the experimental study revealed that defrosting frozen chicken meat using the most common home based thawing practices produced similar color and textural profile values among the cooked samples"


Significant differences:


Microwave and thawing on counter produced this highest drip loss.
Thawing in the refrigerator produced the lowest drip loss.


I would think this supports Julia's advice.