I do see what you mean, but the idea of love as a vital element in the creation of heroes has run throughout DC films thus far.

Without the love of his adopted parents and of Lois Lane, Superman becomes merely an engine of destruction. Accepting that his parents did what they did out of love for him is what brings Cyborg out of self-absorbed seclusion. The love of his parents, for each other and him, and his love for Mera, is what gives Arthur Curry the courage to accept his destiny as Aquaman. The loss of love and the inability to find it again is what renders the Batman dark, ruthless, cynical and careless of his own and others' lives.

You have to ask yourself, has Diana, who has been worthy of all the accolades due an Amazon warrior, ever considered herself worthy of love? After all, her own mother is both stern and distant. If the one night stand was just that, then it means nothing. But is she is loved, truly loved, then she is more than just a warrior, more than a cypher or pawn of fate. Which is good, because Ares is the God of War, and as such, cannot be defeated by a mere warrior.

Myself, I'd have added other memories, as well as Steve. Happy times with her mother and her sister Amazons. All the stuff Harry Potter might need to summon a Patronus.