On the amiibo thing, I still think Intelligent Systems is the best developer when it comes to amiibo usage. The content they give is substantial, yet non-essential. The perfect mix, IMO.
Code Name: S.T.E.A.M. - Allows the player to recruit Marth, Ike, Robin, and Lucina and use them in battle. Non-essential in the sense that basically all their special moves are reskins of moves already in the game, and that they aren't part of the plot. Substantial because they're new units with a neat permadeath gimmick and also give new music. They also wouldn't have been in if not for the amiibo because there was no reason otherwise for Fire Emblem characters to even show up.
Fire Emblem Fates (Birthright, Conquest, Revelation) - Allows the player to permanently recruit Marth, Ike, Robin, and Lucina. Non-essential in the sense that the game has TONS of other units to use, and the storyline isn't changed whether or not they're present. Substantial in that they're four of the most popular characters in the series as usable units, each with their own signature weapon (Falchion, Ragnell, Thoron, Parallel Falchion). Considering Fire Emblem doesn't re-use characters in this way, the amiibo are the only reason they show up.
Fire Emblem Echoes: Shadows of Valentia - Allows the player to summon one-turn illusions of Marth, Ike, Robin, Lucina, Roy, Corrin (male), Corrin (female), Alm, and Celica. While a bit more shallow than in Fates, this is likely due to the fact that adding that many new units to a remake without changing much else could disrupt game balance (for reference, Alm and Celica's paths only added one new character each). Non-essential because they're one-turn phantoms that just help players out of tough spots.Theyre only there because of the amiibo. The Alm and Celica amiibo also unlock one special dungeon each, which is the closest thing to something substantial behind disc locked content, but the content of the dungeons is pretty non-essential, and nothing compared to, say, Wolf Link in Breath of the Wild.
They're easily the developer that gives amiibo owners the most bang for their buck while also not punishing those who don't have any Fire Emblem amiibo. Stock was an issue, but it's definitely better now for the most part.