The majority of the lore based events have a clear loser and a clear winner, at least in the eyes of the community. The edgelord will win pretty much 99% of the time. That's why the VS event this year was swapped to something a little more iconic and more difficult to immediately predict.
Yasuo VS Riven? Yasuo won, we all knew this. He's the edgelord above all edgelords, the biggest meme and frustration on the boards. Half the people love Yasuo because "OMFGSAMURAIRONINOMFG" and the other half are tryhards who think he's the most skillful champion in the game when they can use Windwall.
Garen VS Darius? Darius won, OBVIOUSLY. He's the edgelord, and with how the lore has painted Garen as being a dick larger than Draven's ego in the minds of players, they obviously sided with Darius, who is actually shown with a range of emotion in his lore content.
So yeah, the events had become extremely predictable. Jayce VS Viktor? Viktor wins, because his lore makes him more relatable and less of a dick than Jayce's. Shen VS Zed? Zed wins IMMEDIATELY because he's the edgelord, and people would rather throw in with the militant Hot Topic salesman than the teacher at an academy who "represents authority that I must disobey!1!1!!" Thresh VS Lucian? Thresh wins, he's the edgier one, also the undead monster, and has seen much more stable popularity than Lucian ever dreamed of. Also 100% Wifesteal. Rengar VS Kha'Zix? Rengar wins, he's more relatable as a character, not just some mindless insect out for the kill, and he's also our edgier stabcat. Kayle VS Morgana? HAHAHA. With Kayle's new lore, she's an immediate loss. She's painted as a Grade A BITCH, and most people already didn't like her extremism in the old lore. Morgana's new lore makes her more lovable, without any immediate flaws, so of course she wins this.
Diana and Leona wouldn't happen anymore, because they are no longer at odds in the lore.
But you see what I mean? They're predictable and there's no real contest in Champion VS Champion contests. If there was like a knockout style event that followed several champions and battles against each other, finalizing in one battle against the winners of both sides, then maybe, but as just one versus one it's brainless.
VS 
but i can get behind Cats VS Dogs
already got some fairly expensive skins last year. I know 
is getting a dog skin, but it's not going to feel like much of a VS event if we have fish wearing dog skins and lord knows what wearing cat skins when we have actual dog-ISH:
