I think the controversy stems mainly from Riot not communicating their intentions well enough. People were expecting their holiday skins to be shipped (or made available from the legacy vault) on the celebration day. However, for some peculiar reason, Riot decided to only release the Harrowing story and not tell the out-of-PBE fanbase that the holiday skins will be delayed. Certain people seem to get very upset when their holiday events don't arrive on time, as one could experience two years ago.
It might seem that the Worlds were the main reason why Riot missed the Harrowing date this year, and I am afraid that actually could be the reason. Tbh, I wouldn't be surprised if Tencent, a Chinese corporation, directed Riot to ommit the Halloween event in favor of Worlds, as the holiday isn't very popular in the Far East and could theoretically affect the amount of people watching the finals. I'm not an economist, but I could say China and Korea are a pretty big market for computer games.