No, it's not. Well, from your side it seems to be. The objective way to look at this thread is that there are multiple sides:
(1) I'm not OK with Nintendo locking content behind the amiibo.
(2) I'm not OK with it, but will feel better if there's a non-amiibo way to unlock this.
(3) I'm OK with it
(4) Not only I'm I OK with it, I'm excited for what the amiibo will do in this game and in Zelda U
(5) People in camp #1, stop whining and deal with it (I'm not making this up, this is the tone in a lot of responses, and one of JoeM86's posts in this thread actually has the words "deal with it" in it).
Personally, I'm somewhere between #1 and #2. The level of Nintendo favoritism in this thread is understandable... but unfortunate. No matter how you look at this, this is on-disc DLC. A similar practice by Capcom with Street Fighter x Tekken got them a massive amount of (justified) backlash here on GAF, at least from what I remember. If it were any of the other usual publishing villains, like EA or Ubisoft, this would also get (again, deserved) backlash and criticism.
But it's Nintendo, so it's cool yo./s
Its on-disc content that you can sell back once you are done with it and get your money back. Again, can you do that with DLC? The answer is no, no you can't.