I know KS/KSE might not get better performance than KRE does because KS/KSE has Log Viewer which could make performance worse. See Log Viewer slows down your tests. How to prevent it?. But I am not sure if @duylong mean that there could be any other factors (other than Log Viewer) that makes KS/KSE slower than KRE.
What is the factor(s) you can think of that makes KS/KSE slower than KRE?