It still wasn't a main style Kirby game, and an exclusive amiibo wouldn't sell unless they intentionally didn't release one of the Smash series, unless it was like Knuckle Joe or something but even then that's not a big selling enough name to push bundles. So no, the stars would likely never align to make Rainbow Curse a "hit" by traditional means.

There aren't enough amiibo collectors to make a game a hit on amiibo alone. Even Chibi Robo will sell pretty poorly despite collectors diving in.

Don't think it would matter.  

It actually did come with amiibo support, but this is missing the money for the trees.

The true issue here was that the gameplay was more suited for 3DS, just like how Code Name STEAM or Kid Icarus: Uprising would've fit better on Wii U.

That's because this generation doesn't respect the Chibi Robo IP.

Do Kirby games sell a lot to begin with?

A Clay Kirby would look to similar to the original Kirby so probably not.. Would be neat if a Kirby Amiibo was bundled in the game though

Nope, because Rainbow Curse simply wasn't the Kirby game everyone wanted! If only Ninty would make a 3D Kirby game..

I'm guessing that an exclusive amiibo bundle would have pushed the game an extra 50%.

It would have been cool if they game came bundled with Clay Kirby...

This. Even if Codename S.T.E.A.M. would have bombed either way.