You're writing something that is at best accidentally misleading and at worst confidentially incorrect.

What is your formal definition of "optimal strategy"? A Nash equilibrium is considered optimal in the sense that it's a state where no one can gain an advantage by deviating from the equilibrium.

Sure, if your opponents don't play the Nash equilibrium, there is room to exploit that deviation and potentially gain more than what you would get from playing the Nash equilibrium. However, you also make yourself exploitable in return, so I don't think you're presenting the whole picture here.