Though I own all the Splatoon Amiibo, I think it is a good think that they didn't hide Storymode content behind the Amiibo.
In Splatoon 1, the Storymode is UTTERLY boring without the Amiibo. So that is an improvement.
I generally don't like Nintendo hiding important content *cough Epona*, behind Amiibo. I am an adult, I have enough money to buy them all, but it feels like exploiting young people. For Splatoon 1, you'd have to cash out at least €45 on top of the main game to get all the single player content (Roller, Charger, Time Trials). I think that is just a bit too much for a game mode that isn't TOO interesting to begin with.