So I saw this post and responded on the messages but also wanted to post here in 1 post:
To be fair, if you think about it, they did earn these titles. They just did maybe 1 or 2 acts.
Peter: wolfsbane, protected his family repeatedly; leading the narnians, a race he has nothing to do with at the age of 14; leads a battle, wins said battle with Aslan's help; doesn't lose faith even after he hears Aslan is dead.
Susan: logical about the river; tried to take into consideration everyone's emotions, the home. her family; was kind with Lucy when she was nostalgic; and every time little sis misses home (yes she was also rude to Ed, that changes over the events that happen); went with Lu to go with Aslan, held and cried over Aslan, with Lu, not trying to harden her heart, although that would've been easier (and more cruel); comforted Lu in the witches castle, with Tumnes, the hug at the end
Edmund: was a brat due to neglect and WW2 trauma and took it put on his siblings, but after he was dealt with consequences, he tried to better himself; the guilt on his face when he accidentally gave up The Stone Table to protect Tumnes; trying to save the butterfly, trying to protect the fox, fighting the witch, breaking the wand which gave her an unfair advantage over his army, almost died to correct his mistake
Lucy: strongest in faith in Spare Oom and Narnia; the first to enter, due to her faith; sees the good in Tumnus even after he admitted to betraying her; forgives Ed so quick for lying about Narnia and the treachery, even when he snarked at her; first to jump to wanting to help the narnians; wanted to go to war with her tiny dagger, bless her tiny heart; wanted to join the battle after Aslan was revived, did not hesitate to help with her cordial, to heal as many people as she could.
it may not have been much, over the course of the film and it may not have been expected, but they did still earn their titles, each of them.