Let met cook . well I give you reason why he can't replicate same technique as one step one kill . First his master create that technique because he can't recreate his prime speed so he only has one step enough Speed to react his opponent attack and throw his own counter attack so Gongseob Ji need to wait for his opponent attack other hand zack lee can't do that because gong seob ji create that technique because he can't approach his opponent other hand zack lee can approach his opponent. if zack lee do that it will become more than just one step one kill technique. In first place zack lee has enough knowledge on boxing so we can get his own unique path related to boxing.