Aside from a new skin in SMM you are right, it is the same. I just got it cause I love the design of Yarn Yoshi and the big one looks a lot better.
This is debatable. Skins mean a lot to some people (not me personally, but to others they do). I don't think anybody would argue the 8-bit Mario unlock in SMM is minor though. The mega mushroom completely changes the way the game plays when used and completely revamps the way you'll have to design your levels. The levels I've uploaded using it have by far been the most popular, probably because they allow things that simply can't be done otherwise like running through walls and breaking bricks under you. It's a huge addition because it's such a game changer, and the fact that it's locked behind amiibo is disgusting.
Then we have crap like Shovel Knight co-op and extra levels in that Megaman game and Splatoon. Nintendo and co. are becoming more and more brazen with the amiibo paywall bullshit. To this day I can't fathom why they can't just be collectible display pieces.
Which skin does the giant one give you that's different from the little guy? I won't bother espousing my extreme disappointment in
SMM's lack of multiplayer/co-op.
For me, I like the skins. They're cool. However, they're not $10-40 apiece-cool.
Halo 5, there are HUNDREDS (maybe 1,000+) visual variants for things from emblems to armor to guns to assassination animations, and I don't have to purchase those. However, just to make Yoshi blue in
YWW, I had to spend $17 (minus GCU, plus tax). Like I said, $40 just to have the functionally similar giant Yoshi (and even $32 with that coupon) is a tough sell.
But it's like you said, there are some nice additions. However, you're talking, what, 5% of the amiibo that functionally offer something compelling? I'll grant you the idea that to hell with any idea of hiding major game features (co-op, for example) behind a $15 piece of plastic, that'd piss me off. However, I can't even take Charizard into
Yoshi's Woolly World. Really, my expectation would be that if the amiibo is supported in the game, I can play as that character. Rather than see
Mario Kart support 20 amiibo with Mii costumes (who the hell ever wants to be the Mii characters?), I'd like to see them give support to 5-10 amiibo where it adds the character as a playable racer. Instead of a tiny square that supports maybe 10 amiibo and support for some dumb points stuff with another 30 amiibo, they could have had the amiibo add 10-20 playable characters (with full animations, not wobbly plastic crap) on actual game boards (and removed the car travel crap). They went for quantity support that is mostly underwhelming, rather than truly leveraging amiibo into something beyond a tiny novelty and collectible intrigue (killed by restocks for many, it seems).
Pokken Tournament is coming. They could (maybe even SHOULD) have made it like
Killer Instinct, where you can get a number of Pokemon (maybe the rumored 10 supported character) supported in the base game (maybe free like
KI?), then churned out 100 of the best Pokemon as amiibo to play in the games. They have, like, a dozen
Mario Tennis characters, which has me almost entirely turned off to dropping $50 on that game (again, minus GCU, plus tax). If I could throw on blue Yarn Yoshi and play as him, if I could buy Charizard and play as him, they'd have probably sold me on another couple of games and a dozen amiibo, and I'd imagine many others are like me (would buy more games if amiibo support was good, while also getting the amiibo of our favorite characters).