While I am a bit skeptical if a lore retcon on this scale was necessary, I do understand why they did that(lots of new stories wouldn't be possible in the old lore) and think that the end result is a lot more solid than the previous lore, especially the world building, which was almost nonexistent in the previous lore.
The only retcons I really didn't like were I think
and
. I don't think that Zacs parents needed to be dead, that feels honestly a bit generic and removes an interesting element from Zacs lore and Shyvanas new lore feels rather awkward with the removal of her dragon dad and Shyvanas mother having unclear motivations.
Targon, the darkins and the angels are also a mixed bag, where I do like some elements of the updated stories, but dislike others.
I also feel like Riot has lately slowed down with actual lore updates, as several champions are still missing their new bios and color stories, which is in my opinion unacceptable. Bandle City has also been left in the dust, which I really don't like.
Sure they do release some new stories from time to time, like Lissandras dream-story, but I feel like updates should take priority over new stories(and no the dream-thief does not count as Lissandras color story).