Unless they are planning to add Jarvan III to the game or give him huge development then I think it's pretty pointless to not have Jarvan IV as king and it makes Demacia also less developed as a result.
I like that he's a Prince. I feel like J3 sending his son to do these things is helping him learn how to be King, sort of like how Corleone starts training his son to "run the business" as the Godfather before he dies. Plus Princes generally have more room to grow, so it makes him interesting as a character.
Lastly, I like that we don't always have the leader of each respective faction: it's sorta weird that Noxus, Freljord, Ancient Shurima all have leaders fit for battle. For one thing, I would like to hear more about leaders who aren't elected based on their "power" in battle: this makes sense for places like Noxus, Demacia and Freljord, but somewhere like Piltover have different ideas about what it means to be powerful. And second, we get to see J4 grow into the position, rather than just have it from the get go like a handful of other Champions do. (Without sounding bitter, this didn't used to be the case. Swain, Ashe and Trynd didn't start as leaders of their respective factions in the old lore, but since that stuff is pretty much ignored by most of Riot's lore team, it's not relevant anymore.)
I wouldn't mind seeing him BECOME king eventually, but I'd like that to be a well-earned character moment.
Well it is important to remember/ understand that the Demacia LU had it's main focus set well away from the kingdom's monarchy and current rulership. So as much as I'm sure we're all very gutted III or any of the previous kings didn't make it into the overarching narrative of the update (like not even a mention during a Galio flashback!) yet that doesn't mean III is redundant by any means. Unfortunately it did mean he's redundant for that lore update, but otherwise I agree since the "coming of age" aspect for J4 doesn't work as great until we can see the predecessor history as well.
I would have loved at the very, very least if one of the talented concept artist did like a royal family portrait or something. Get a good look at the Lightshields in their Snowdown sweaters or what ever the Runeterrian equivalent of Christmas is.
