To account for sample size differences, let's use 95% Confidence Interval:
Retro true TvZ win% could be anywhere between 56.2% to 58%
Fighting Spirit true TvZ winrate could be between 50.1% to 53.5%
I can be (95%) certain that Retro has worse TvZ balance than FS now.
According to Korean Namuwiki, Retro was supposed to help Zergs in ZvT. What happened?