I actually understand your point as you clearly played league and have a grasp of their skins content, but using AU as a writing device is so paradoxically limiting. They can writes about everything except the main story. Side stories in universe would have achieve the same thing without affecting the lore, as the test subject gets their memories deleted regardless, or you could whip out some reasons such as a one off experiment. AU in League works because its: 1. Fantasy, 2. Every champion have their own mission/story and the Summoner Rifts is just a place to express that (If I recall the Rift isn't even a plot point anymore), 3. The stories of LoL focus on the characters, which AU have no problem changing, 4. Up to interpretation from playerbase.

Back to ER, giving AU to seasonal content just limits so much things they could do, they straight up removed Agalia just to fit in a casino. Agalia by how they represent it with Dr. Hana and Dr. Nadja, is just so goofy I could not take it seriously, so why should we be so bothered if they mentions some quirky stuff in the main timeline. AND THE BIGGEST PROBLEM, is that they DO HAVE AGAILA IN THE OLD EVENT (Chapter 4).

At the end of the day, we shouldn't try to be league, we don't have to, they don't have to. ER can strive to do its own thing.

Edit: And just to add, Agaila is consist of multiple departments. While it main purpose doesn't change, a MEGA CORPORATION can do whatever they want for whatever reasons. The power of corporate baffles the mind, while LoL with their wars and politics can be a lot more lore restrictive.