Is the issue here that Superman may well be seen as a beacon of hope 'in universe' but to a majority of the audience he didn't for one rosy second.
I think that speaks more to what people mistake or misunderstand as hope, honestly.
BvS does not sell Superman to the audience as a positive character. The overwhelming response to him across the board was that he was not the shining beacon of light that Superman should be. There was just too much mopey, violent Superman, and nowhere near enough saviour Superman.
A character who is mopey yet still steps forward to save people, takes a leap of faith on humanity, continues to save people, attempts to engage in conversation about his role in the world, decides to endure anything that comes because this is his world, and does so by dying for it is what makes this Superman, in particular, a shining beacon of light. Hope can only exist within despair; light shines brightest in darkness. Superman is a beacon because he overcomes fear, doubt, guilt, and hopelessness. And he's no more violent than Reeve's Superman, so that criticism doesn't work as an explanation.
You can make arguments all day long about how people within the narrative think he's a beacon of light, but if that hasn't translated to the audience (and it really hasn't) then people can't be blamed for feeling like what Batfleck says in the JL trailer rings hollow.
We saw how Clark saved Pete and in doing so made him better. We saw how Clark's legend as a guardian angel and his story about Jonathan moved Lois -- an ambitious and successful journalist who posted her mysterious alien savior story on Woodburn's cancerous blog -- to drop her follow up story that intended to reveal everything about Clark to the world. We saw how Superman's humility in surrender and allegiance in battle convinced Colonel Hardy, General Swanwick, Captain Ferris, and Dr. Hamilton to trust him and work with him to defeat Zod. We saw how Superman's love for his mother gave Batman another chance to fulfill the promise of the good man his once was, and later how his sacrifice restored Bruce's faith in men and helped him embrace not just aliens but metahumans and gods as friends and allies. These characters don't think they are better because of Superman; they know they are better. We've seen them be better.
So you can make arguments all day long about how the line rings hollow because the films didn't work for you, but at some point you have to ask yourself why hope and inspiration has to fit into neat boxes and predetermined tropes in order for it to register as real. The Superman I love is a hero whose beacon shines brightest when he makes a difference in the lives of the bullies, the broken, and the lost. He's the hero who doesn't need the accolades of adoring crowds to find validation and is uncomfortable with deification of any kind. If Superman can find hope and the will to keep going, to be humble, to apologize, to trust, to protect his enemies, to keep saving, to choose our world as his world, and to keep sacrificing, then what greater hope can there be?
Hope masquerading as joy, perhaps? Hope as near universal love and acceptance? Hope as fame? For Reeve's Superman that sentimental version of hope walked the tightrope of selfishness and vanity. He was willing to give it all up for love, and when that couldn't last, he killed his enemy, wiped his beloved's mind of her memories, and beat up his bully rather than show him a better way. The greatest example of his ability to inspire hope and make someone better was Miss Tessmacher who saved his life in exchange for the protection of her family. It is only a shade of Superman's inspirational effect on Batman, however. But he was confident, happy, extroverted, witty, and charming, right? I guess that is what passes as hope these days. Pity.