One thing people get wrong about the Trinity is that Clark/Superman isn't the optimist.
He talks about having hope and believing in people. But really he is a pessimist who tries to be optimistic. who is always struggling with a fear people can't change and can't be saved.
Bruce/Batman is the optimist. He is always sure people can change, be better, are better, that things will be better in the morning.
It's only the fact Clark loves humans, earth and everything about the average life that he keeps that small seed of hope.
Going on to Diana, Diana isn't a pessimist or an optimist. People say she is the beacon of Truth in the Justice League. But Diana isn't just driven by a need to bring truth to light. Honestly Diana is a bit of a fatalist.
She is basically immortal, has seen the worst and the best of humanity and fully believes everyone should have a chance to live the best life possible because it will be over before they know it. She knows that life is imperfect and fleeting and everyone she loves will one day die, but she wants to fight so they can have as many seconds of love and happiness they can.
It's why they work so well as a trio.
Clark wants to believe in humanity like Bruce does, Bruce wants to love every second of life like Diana does and Diana wants to fight for that reason to have hope everyday like Clark does.