You should have a problem for not simply offering as DLC on the eShop then. Why can't they offer both? It's utter shite that they are tying content to a finite resource, for an object you might not necessarily want. The DLC sales can fund said content too. This logic makes no sense.
Yeah you're right they could offer it on the eshop, but I don't think that discredits the fact that this possibly exists due to the amiibo. I feel like they had the mock ups for the amiibo, sat in a meeting and said, what can we offer with this? Someone said "well we added hard mode in TP, we could do that again, that way people can't complain about amiibo only offering cosmetic changes. Oh and add the fusion suit too". The decision to add it to the eshop would've came later. I don't know, again I don't think that's too far fetched a thought. It would be cool if they added it to the eshop as well like a lot of you are suggesting.
I think if anything, this brings up a bigger question of what amiibo should be used for. It seems as if skins aren't enough for most, but this has clearly crossed the line for a lot of you. I like this idea of also offering the content as DLC as an alternative to amiibo, it seems most would be happy with that solution
Edit: Like if could've bought the BOTW DLC in the form of a giant Bokoblin plushie for $5 more than the normal price, I would've done that