Let's Talk Cheerful Characters
Riot makes very good cheery characters in the game. Zoe is cute, her VO is adorable and obnoxious, and she's very lighthearted and silly. Ivern, Lulu, and Zac are very similar in this regard, and they have very fun personalities that are refreshing to see after all the dark characters in the game.
That said, I seek to understand why Riot has difficulty letting characters simply be light and carefree. Zoe, for instance, nukes a town for fun. Ivern, despite being the resident Bob Ross character, used to be a murderous brigand who tried to destroy a sacred tree after carving a brutal path through Ionia. Zac's parents, the people who adopted and loved him, died horrible deaths, leaving him alone in the dank pipes of Zaun. Lulu is completely sociopathic, and thinks that turning kids into flora and fauna for games is "fun." None of the cheerful characters in League are actually truly cheerful. They're all tarnished with these awful flaws and horrible atrocities in their past, and it completely contradicts the fun and peppiness they're portraying in the game.
Braum, so far, is the only instance of a silly, carefree character in the game without some dark, awful event in his past. So I'd like to see Riot take a break for a while from giving fun characters such dark pasts. It's fine, now and again to have a dark moment in someone's past. But when almost every recent character who's currently cheery and peppy is hiding something sadistic and homicidal in their closets, it starts to become clichéd and unintuitive in terms of story telling. Zac, for instance, was very much a richer character because he had living parents to go home to - it was unique and showcased a certain kind of love that you don't see a lot in games. Having dead parents now doesn't enrich him as a character, and makes you feel sad for someone who's such a goofy, fun character. Ivern, similarly could have worked wonderfully as just being this perpetually happy and oblivious nature spirit wandering the world, so tainting his backstory with being a former murderer detracts heavily from the myth and persona he gives us in game.
This leads me around to an upcoming carefree set of characters - Nunu and Willump. They have light lore at the moment that isn't that developed, but it does give us a bit of a heartwarming story of a boy befriending a yeti and becoming unlikely friends. I'd like to see this developed, without plunging them into the darkness. Riot has shown us with Braum that they can be capable of cheery characters without dark pasts, so it's time to go back to that with Nunu and Willump. People are rich and diverse, and while perfect happy stories aren't typically that deep or intriguing, against a backdrop like League's expansive lore, such stories are foils and give us a view that we don't see a lot in the game. The game's very dark in terms of the approach to the story telling, so bring some light in to make the dark's richer and give us a little happiness to go with once in a while.
imo is actually a rather big stand out for what you're after really.
and
also fall into your description of "lighthearted without a dark past", so I don't think it is as bad as you make it out to be.
And stories come along with conflicts oftenly, just having a dude who is just joyful all the time and has never known any struggle gets boring soon, especially if you want several characters for that trope.
? He seems pretty regular but still very cheerful.