• Mario Party has a locked game mode where stages are locked behind Amiibos.
• Mario Kart Wii offered free outfits for your mii. MK8 has more outfits, but all locked behind Amiibos.
• Hyrule Warrior has a weapon locked behind an Amiibo.
Amiibo Party is "locked" because the Amiibos are actually required to play. The mode serves no purpose without them, so you scan an Amiibo in each time you want to play it. The whole point of the mode is that you can save tokens and bases to the Amiibo, and bring it to your friend's house with all of the data intact. Also the boards are not really unlocked either, it's more a case of whichever characters players are using, you are encouraged to figure out a way to decide on what board to use, such as flipping a coin to get your characters board. It's an element of the game. Besides, as you play, you can find "board tokens", so you can mix and match the board as you play (you can even equip these after you first find them, to use at the very beginning of a match - if all four players had Rosalina tokens on their Amiibos, but none of those Amiibos were Rosalina, they could still use the full Rosalina board). I've played on the Rosalina board plenty of times despite never scanning the Amiibo in, for example.
The MK8 outfits are not "disc locked", they were added after the game's release (in the same patch that brought in the Mercedes Benz cars, I believe). They are also not an essential game component, merely cosmetic bonuses that reflect your personal character preferences. If you like Yoshi, you probably buy his Amiibo for Smash or Mario Party and for the sake of having a well made Yoshi figure, and then you get that little cosmetic bonus in MK8. It's not the same as Splatoon, where the big use of the figure is to unlock major game content. Yoshi's main use is to be used in Smash and Mario Party where the data is saved and you can then bring it around.
Hyrule Warriors is developed by Koei Tecmo, not Nintendo, and Koei Tecmo are known for doing DLC with the Warriors franchise, and Hyrule Warriors is no exception. However, once again, none of it was disc locked. Also once again, the Spinner weapon isn't a big deal, because Link has a ton of weapons already, and even more in the larger DLC packs. It is once again a case of you buying the Amiibo for Smash (or other future games where Link has a bigger use), and getting a small bonus in a game made before Amiibos released.