The bulk of Nintendo's first party games aren't developed in-house, though. EOL is published by Nintendo, developed by Arika, will certainly at least have EPD producers attached, and is a license co-owned by Arika and Nintendo. It's as first party as Fire Emblem.
Again, I'm not interested in arguing about the line up this year other than to make the obvious point we don't know the full picture, but Endless Ocean Luminous is objectively and entirely a first party game, published by Nintendo in all regions.