If you think that is actually a reasonable bar for first week sales, i guess prepare to be dissapointed.
Legs have been the main difference in showing switch health software results
Not debuts
In first week, a comparison between the last entry on 3DS (exluding ports, remake and remastered) and on Switch (all numbers are from
Game Data Library) :
Yoshi's New Island (66 225) --> Yoshi's Crafted World (50 007) : -24%
Super Smash Bros. for 3DS (987 239) --> Super Smash Bros. Ultimate (1 238 358) : + 25%
Mario Party Island Tour (135 419) --> Super Mario Party (126 275) : -7%
Mario Tennis Open (124 377) --> Mario Tennis Aces (122 070) : -2%
Kirby Planet Robobop (153 878) --> Kirby Star Allies (223 811) : +45%
Super Mario 3D Land (344 698) --> Super Mario Odyssey (511 625) : +48%
A Link Between Worlds (225 418) --> Breath of the Wild (193 060) : -14%
So yeah, I was wrong: not every game was up in comparison to 3DS, but three games (two if you want to count the best selling Kirby on 3DS) perform well above what they did on 3DS, two games did slighty less and only two games did sharply less, Breath of the wild (a launch title also available on Wii U at the same time) and Yoshi. Even this game is only 24% down.
Fire Emblem Fates did 353 201 in first week. 76% of that would be 268 433, and it would mean that the game would match the percentage drop of the worst selling Switch exclusive yet. So yeah, less than 300 000 in first week would be a bad launch for the game. The IP was bigger than Kirby IP on 3DS, so it would be really disapponting if it did less (or not really better) on Switch.