After playing this opioid of a game for 3 months I just discovered that the order in which you choose your PVP attack (and defense) heros actually matters.
I'm not talking about Fast / Normal / Slow; I'm talking about having 2 Normal speed. The order in which you pick is the order in which they attack.
I'm sure this is just common sense to everyone else, but it was an epiphany to me.
Sharing what I can...