Actually I think I'm okay with the lore retcon, here's why you should be too
So, a quick glance at the billions of other forum posts should tell you why removing the Institute of War is a terrible idea. And, well, yeah. It is. If you're planning to make League of Legends stories, that is. It's a great plot device that simultaneously bridges disparate themes and factions while providing a significant, concrete obstacle for characters to work around.
Here's the mental shift that needs to be made in order to see this as a good idea:
Runeterra is not full of League of Legends characters.
League of Legends is a game full of Runeterra characters.
On the players' side of things, all we've seen is the champions in a League of Legends context. It's like if you played Super Smash Bros without ever playing any other Nintendo games. We have all these great characters who work well in a gameplay sense, but who also have very clear and very visible narrative direction.
If you just play Smash Bros, you might pick up Link, see that he has all these neat gadgets, then read his trophy information which talks about how he fights Ganondorf and saves Zelda and all that. It doesn't tell you much about him, but it's all you've got. League of Legends champion lore is roughly on par with Smash Bros trophies in that sense - we know that Nasus and Renekton are brothers who hate each other, and they fight sometimes. Coolio.
But lately (ie. in the past year or two), there have been a few other lore offerings. There's the Freljord event, there are the cinematics, there's the push to make all the new characters have meaningful relationships... It gives us a bit more insight.
To stick with the Smash Bros analogy, imagine it like you played Smash Bros without having played any other Nintendo games, then went and read Brawl in the Family or something. The in-jokes are all character-specific, but there's enough context that you can kind of suss out what's going on.
Since the game's launch, people have been asking for more information. For Smash Bros, you can just pick up a Zelda game to learn Link's story; for League, canon character information is difficult to come by.
The ONLY REASON this retcon would be a good idea is if Riot is planning to broaden its horizons and expand Runeterra beyond League of Legends. That's what's coming. That's why it seems so hard for players and devs to see eye to eye on the lore issue - we're seeing it from fundamentally different perspectives. The devs know that the option is there to, say, make an adventure game about Jayce and Viktor, or to make a hero-based RTS/TBS about the Demacia/Noxus conflict. League of Legends is actually SECONDARY to the universe of Runeterra in the same way that Super Smash Bros is secondary to the Nintendo universe.
And sooner or later, we're gonna be able to see Runeterra the way it's meant to be seen.
(I just hope we don't have to wait too long, because then I'd look like an idiot.)