Welp. It is very rare that I leave a comment in the Leauge of Legends forum, but here I go.
The old lore was decent. I adored the Judgements, the character biographies, and how they were all connected by the Institute of War. It had an okay backstory with why the Institute was formed. However, the old lore wasn't great. There was a lot of room for improvement plot wise. There was no overreaching "big bad" to drive conflict, character growth, or realm expansion. The majority of the conflict was purely political among the city states. eyeballs Noxus and Demacia Thus, when the Institute of War was formed, it effectively killed the primary conflict driver in place. While various champions still had unsolved conflicts, such as Caitlyn searching for the mysterious trouble maker C, Fizz's people just disappearing overnight, among other examples, those weren't enough to drive a story.
Therefore, without a solid source of conflict, it was very hard to expand the world. Story telling wise, a lot of heroes or champions are born in conflict, need conflict to be forged into a hero, or just need difficult trial to make them shine. Or, in some cases, fall into darkness for the anti-hero. In order for Runeterra to grow in a story telling sense, it needed change. Plot wise, the Institute of War, killed all new heroes by removing the primary source of overreaching conflict. Almost all of the older champions were forged into heroes by the very conflict that the Institue of War of ended. The Blood Brothers, for example, were made great by the political conflict between the City States. Riot figured that a retcon and fresh start would fix this. I personally don't see it fixed, instead, I see what the OP mentioned... a jumbled mess.
What we have is a several "Big Bads" to drive conflict. Their purpose and stories are sewn into the story of Runeterra like a badly sewn patchwork quilt. Each piece is valuable and pretty... but when badly put together, it's not very worthwhile. While the old lore was okay, I felt a greater connection with the champions forged in that original lore. While there is a lot of the new lore I personally like, there is such a disconnection that I don't really like very many of the newer champions. While some are interesting, they lack the hook they first few had. I suspect it to be because the story they're in isn't very well constructed overall. If League of Legends lore was a book, the new lore I wouldn't read past chapter three. If the old lore were a book, I would read it through till the end and say "This was okay. I liked it." Then... not read it again because it was okay, not great.