Disagree from a strategic point of view AC makes more sense to delay as Pokemon a guaranteed 15m seller can easily carry the holidays with a smaller project rather than have to large titles cannibalize sales from each other, evergreen titles like AC also don't really rely on holiday boosts look at BOTW these are games people are already planning to get whether on release or down the line hence why they have legs in their sales AC being delayed to the Spring release window is not unusual.
I don't see the two cannibalizing each other. Different subsets. Both games can flourish and make Nintendo a ton of money.
I also don't see why you aren't recognizing that Holiday boosts are big for evergreen titles too. Nintendo would likely lose out on more sales from not releasing Animal Crossing before Christmas than a title like Link's Awakening would make in its lifetime. Something like Link's Awakening, on the other hand, would benefit from a big buildup of its own for a March release with little in the way of competition.
As for carrying the Holidays... I don't think Nintendo has to worry about that either way. Might as well go big this year as Nintendo will essentially be on its own until the next gen starts.