....her conversation with Trevor, and realization that humanity is deeply flawed and the one really responsible for these atrocities
This is what resonated with me the most as well, because it played on the same themes that BvS did and tied it in with Superman's sacrifice and ultimately the founding of the JL.
Initially thinking that mankind is beautiful and that she needs to help save them because Ares is the one doing all of this (WWI) to them, WW comes to the revelation through Steve that humans are indeed fallible; combined with Ares also convincing her that mankind is selfish, weak and unworthy of help by attempting to use Dr. Poison as an example of this. However, through Steve's actions and compassion, she also realizes that there is hope for mankind and that there are reasons to continue fighting for it because in the midst of the darkness, there is indeed light. She realized it was worth saving through the selfless actions of a human themselves; that they're not all "bad".
Similarly, Superman after MoS thought that the world would just accept him and be grateful for his actions in defeating Zod and welcome both him and his help with open arms. However, he begins to realize that everything Jonathan warned him about is indeed coming true and what the ramifications are for his actions and existence, and realizes that perhaps mankind isn't what he initially thought it was. However, despite all of this, he (with the guidance of Jonathan's voice in his head) realizes through Lois that there is indeed light in the darkness, that mankind is indeed worth fighting for and that there is hope for it. Because of this, he is willing to make the play that needs to be made at that moment; even if it means sacrificing himself.
Batman also has a similar story arc to both WW and Superman, in that he initially set out to do good and thought that his actions would rid Gotham of crime for good, but he eventually realized that no matter how hard he tried, he was essentially a gardner in a yard overrun by weeds, where no matter how much he tried to pull them out, one just grew back in its place. No matter how many criminals he caught, another one just took its place. It just wasn't worth it anymore to him because the number of bad people seemed to outnumber the good. He had failed in what he set out to do. However, seeing a God-like being who he initially perceived as an enemy make the sacrificial play for a world that he can easily rule, was what he needed to realize that perhaps it is worth it to continue fighting for good and to not give up.
With WW, in her solo film, she saw Steve, a human, make the sacrificial play out of love for her ("I realized that only love can save the world"). Now to see someone of her equal or possibly even greater also make the sacrificial play because he felt that it was worth making for mankind, and to see that he too was loved by seeing someone (Lois) weeping over his loss, just as she had wept for Steve, inspired her and also inspired Batman.
All three of the marquee JL characters all come from different backgrounds, but in a way, all took the exact same path by having the same arc to their stories through enduring the same tribulations, conflicts, struggles and trials that tested their fortitude, albeit through different scenarios, to get to where they are now and unite to fight for the same common cause. Despite what many think, I personally think that's great character development and maturity.
