and at what point did we get the three titles announced that cemented the 3DS's return from the edge of the grave (along with price cut) ?
Mario Kart was announced at E3 2010, over eight months before 3DS launched in any territory. Mario 3D Land was announced at GDC 2011, a week or so after the Japanese launch. The existence of both, and their ability to "save" 3DS from "the edge of the grave" was a foregone conclusion in any case, because Nintendo, unlike Sony, actually has a stable of first-party IPs that are guaranteed to sell millions in every territory, has a good recent track record of creating new hit IPs, and isn't dependent on third-party support to make its handhelds commercially viable platforms.
MH3G/MH4 weren't announced until September, sure, but 3DS didn't need support of that caliber as much as Vita did (and still does).
a lot of times, hits come from the unlikeliest of places. the third gta made everyone do sandbox games for 5 years. pokemon launched on a dead system and became the best-selling franchise since mario. brain age started off doing 40k a week and then kept doing that for years. i don't think people could have predicted mhp2g's success could have been predicted by too many either.
Due to development realities, we can realistically rule out any Vita (or 3DS) megahit coming from Western third parties. Other than MHP, which surprise hit IPs, of the impact necessary to significantly shift the market in the direction of the platform they appeared on, have originated from Japanese publishers other than Nintendo in the last decade?