I'm just gonna link to a comment (
https://mangadex.org/thread/268985/7/#post_2431021) I've made in regards to Jiho being the ML over Chunyoung in the past and how it relates to one of the themes of the story because I don't wanna type that up again.
I find it almost comical how quick some people are to undermine Jiho without even knowing all the things that happen before we even get anywhere near the ending. It almost always boils down to what is basically "he's not Chunyoung so it sucks/he's worse," with frequent mentions of "it makes no sense" and assumptions that "the author did it for shock value" as if they're certain there's going to be no buildup whatsoever for Jiho, which is so very wrong.
Why not let the story play out before you jump to conclusions? Especially about a character that hasn't even been given the focus yet. Sure, you might think it doesn't make sense
now but that doesn't mean it won't make sense in the future. This isn't even one-fifth into the story yet. What you know is a drop, what you don't know is an ocean. Jiho in particular is a character you can't pass judgment on this early into the story because he doesn't do things in a flashy manner and doesn't like to flaunt his emotions or innermost thoughts.
I understand that a lot of people don't read the novel, but I implore everyone to keep an open mind about all the characters, Ruda and Jiho especially - Ruda because he redeems himself big time and Jiho because people who read second-hand spoilers are unfairly biased against him when he's very layered and nuanced underneath all that sarcasm and out of the 4HKs and Yeoryeong, probably has the most varied and fleshed out relationships with other characters. People are so quick to discredit him because He's Not Chunyoung. The baseless dismissiveness is downright annoying. Chunyoung might've been the First Guy™ introduced, but Jiho gets a lot of focus in the upcoming arcs.
If you pay attention in just the first 63 chapters of the manhwa alone, there are a bunch of subtle hints that Jiho likes Dani, not Yeoryeong (this is also true of the novel). People are only even slightly surprised because (1) right from the get-go, Dani instills her bias on us by writing Jiho off as Yeoryeong's male lead and (2) the aforementioned subtlety with which Jiho does everything and how he tends to hide his innermost thoughts.
And while Chunyoung is being built up in the foreground, the same thing is actually happening with Jiho but much more quietly. They were set up as foils from the very beginning with the contrast only growing more stark as the story goes on. Refer to chapters 21-22 of the manhwa as just one example; when presented with the fact that Dani is hiding a secret from them, Chunyoung and Jiho's reactions are juxtaposed. Chunyoung presses her for answers and doubts her, which I don't blame him for. Jiho, though, knows Dani will close her heart even more if you keep pressing her, which is why he relents and reluctantly agrees to her request of acting like strangers in high school. He implicitly trusts that she has a good reason for it. There is no blueballing or shock factor with Jiho. The author knew what she was doing with his character and it shows, particularly from how his behaviour and mindset from early on are delved into by the midpoint of the story.
Also, you're saying that the author, who introduced very early on the fact that Dani could just up and disappear from their lives and feels like she's undergoing an existential crisis, and in general treats the isekai trope with a lot more gravity than most isekai stories do, planned this out to be just a lighthearted story? I kind of doubt that.
As for Dani's reactions to Jiho being more placid, it's because her relationship with him is much more easygoing than the one she has with Chunyoung. She doesn't worry about saying something that might offend Jiho so she kind of says whatever she wants. It's a sign that they're quite close, even though she can be unintentionally insensitive towards him at times. Conversely, recall how Dani talks about her relationship with Chunyoung: she said it's one where they just kind of revolve around each other from a distance, never getting too close, but also never straying too far. Because Chunyoung said he liked her for having zero interest in him, Dani closed her heart and decided never to push his boundaries. She was afraid of doing something that would boot her out of Chunyoung's good graces. IMO, this is also why Chunyoung is introduced first - because what he said to Dani that day in their first year of middle school had long-lasting repercussions on Dani's mindset that we can see even now.
Her dynamic with Jiho is completely different. It hasn't been mentioned in the webtoon yet, but when she talks about her friendship with Jiho in the novel, you see, again, why he and Chunyoung are foils. Instead of making Dani close off her heart, Jiho was always gradually chipping away at the walls she put up instead - by disarming her defenses with sarcastic jokes. Turns out this was a double-edged sword for Jiho because while it allowed him to get closer to her and form the comfy friendship they have now, it also made it that much harder for Dani to take him seriously even when he drops the jokes and is being completely sincere with her.