So apparently, despite having over 400 exclusive games, the GBC is not a new generation to some because there were cross-gen games released for it that also worked on the original Game Boy, just with less features.
Okay, well, the Zelda Oracles games came out after the GBA was out, and have an extra feature (a shop) if played on a GBA. Much like how you got extra features on a cross-gen Black cart GBC game.
So I guess that is proof the GBA was a GBC revision?
Those games only came because of how well it sold. Let's not kid ourselves. Its sales and consequent exclusives are the only thing that differentiates it from DSi or n3DS. Last I checked, sales didn't affect which generation something is. If the n3DS had completely eclipsed the 3DS and the exclusives had sold like hotcakes and warranted more exclusives being made it would be in the same situation as the GBC... ie, a massively successful revision.
New 3DS consoles have sold millions, maybe even tens of millions. Yet only one retail exclusive has been released, plus some SNES games on the eshop. Apart from that one retail release, every single 3DS game released post-N3DS still works on the original 3DS.
The distinction is not sales, but age. The Game Boy was 9 years old when the GBC was released. GBC sales took off, but did not eclipse original Game Boy sales. The GBC's backward compatibility was done purely to support the success of Pokemon, as the GB had seen a very late sales uptick because of it.
But 3DS was only 3.5 years old when the N3DS was released. It was just a new model to spur sales. The extra power is used (and was most likely added) primarily to make the UI run better.
At the very least, GBC is a special case. A 1.6 generational leap. It is certainly much closer to a new gen than DSi and N3DS were.