Yes Amiibos can be viewed as DLC, but what is inherently wrong with DLC? IMO Nothing if the DLC is is a good value and doesn't subtract from the value of the regular game. Great examples of DLC include Red Dead Redemption: Undead Nightmare or GTAIV: The Ballad of Gay Tony.
So far, Nintendo has not released any games (that I have played) where most content is amiibo locked. In fact, the value of an amiibo seems to go up as time goes on, as compatible games increase in quantity. If you think that the quality of the DLC that comes with the amiibo is poor (i.e. a skin for yoshi wooly world) you should also take into account that these rewards seem to add with each new game (amiibos now can give you skins for mario kart, SMM, Yoshi, and others I think).
Also with Amiibos, you have a tangible representation of your DLC. Unlike other DLC, you can resell it, trade it, etc. it doest have any DRM. Id rather have all DLC be physical if it meant I could sell it eventually.
Full disclosure: I have Mario Kart 8, Smash, and splatoon that use amiibos. I haven't played mario party, or amiibo festival, so I don't know if those games handle amiibos very poorly or not
Proud Owner of:
Atari: 2600 5200 Jaguar
Sega: Master System Genesis (W/CD) Saturn Dreamcast Game Gear
Nintendo: NES SNES N64 Gamecube WII WIIU GB GBA(W/e-Reader) DS(i) 3DS
Sony: PS1 PS2 PS3 PS4(W/VR) PSP
Microsoft: XBOX XBOX360
Other: Colecovision, TurboGrafx-16, OUYA, R-Zone Super Screen, Xavix, Intellivision
Windows 10 w/ 12GB RAM, first Gen i7 processor, and 480 GTX; MacBook Air