I guess that 4s Main will attack faster than 3s Main.

It seems, we were wrong about this. I've 65lv and my friend has 63lv, both have 705 Initiative on Main, same positioning, I've 2k power more. But when we fight each other, it is pretty much random. Once I'm faster, then again he is faster. So it's random, or who will press the *on faster.