Argument 1: "Why are the other gamemodes not an issue?"
There is nothing wrong with the currently available modes due to how little the actual game's rules change: ARAM is just norms with only one lane and random champions, there's virtually no balance changes besides a few items gone, and Twisted Treeline is just 3v3 norms with an altar gimmick. URF, on the other hand, requires a lot more work to keep in check, due to the fundamental design of URF, being for things to be overpowered.
Argument 2: "Playerbases are never split from variety."
A good example of splitting a playerbase is Evolve. Microtransaction hell aside, you know how many modes that had? Due to all the modes in the game, the little playerbase they did have was split up across all of them; some people only played Arena, some only played Hunt, some only played Rescue, etc. This resulted in VERY long queue times for games, due to players not playing the same modes as eachother.
Overwatch can get away with this because of 2 reasons: The gamemodes are switched up from time to time, and almost all of the gamemodes are fundamentally the same exact thing as the normal game, with little difference from Quick Play, with the exception of the event gamemodes and Deathmatch.
Argument 3: "URF is meant to be broken."
Sure, people play URF because it's broken, but as broken as it is, it STILL needs balancing, due to some champions being beyond broken. A LOT of champions have actually had tuning in their kit done to make them good/less OP in URF. People complained how OP a lot of champions are the first time around, and Riot realized this. Some champs have been balanced to be good, Like Aurelion Sol, for example.
Argument 4: "My queue times are A LOT shorter than other gamemodes!"
Your queue times are instant because almost nobody is playing other gamemodes at that time. URF makes other gamemode queue times spike HEAVILY, which further proves my point that it splits the playerbase.
Argument 5: "You're just salty and kissing Riot's ass for every decision that they make."
Salty? Because Riot is getting called out? I've called out Riot myself, multiple times. Riot often does deserve to be called out. The Orange Essence situation, of the disenchant OE being too low? Sure, call them out, it's something that needs to be discussed. Lore retcon? Sure, go for it. Attempting to remove item sets from the new client (Which, discussing it did work out!)? Please, discuss. But this is not one of those times. While I love URF, I don't think it would work good as a permanent gamemode.
You're just angry about Riot removing URF, which is why you've tried to insult me throughout your entire post.