Humans don't have instincts, except a little baby's instinct to suckle. An instinct is a pre-programmed behavior, not a desire. Only non-human animals have instincts.
Motivation is never something to overcome. Motivation is power. You work with it.
By "willpower" people usually mean ability to force yourself to do something you aren't motivated to do - you shouldn't try to do that, it's operator error of the human system.
of course humans have instincts, we're an animal like any other, just because some try to do anything they can to suppress those instincts doesn't mean it's not there
Those are not complex behaviors. An instinct is a complex behavior, like migrating for the winter or building a nest.
The problem with claiming that humans have instincts is that it gives cover for bad theories of mind. For instance, the Nazis believed Jewish people have Jewish minds and German people have German minds; many Marxists have held that bourgeoisie have bourgeois minds. In reality, the human mind is a blank slate, in terms of knowledge and beliefs.
Motivation is never something to overcome. Motivation is power. You work with it.
By "willpower" people usually mean ability to force yourself to do something you aren't motivated to do - you shouldn't try to do that, it's operator error of the human system.