If they are dropping support you see it by what they're MAKING not by what they're RELEASING. Especially when a game like Fire Emblem is so far removed from development the next iteration of FE is likely already in full development(and it won't be a 3DS game...)
What does 3rd party games have to do with Nintendo's support at all? Does Sony still support the PS3 and Vita because both get Japanese 3rd party games? IMO they sure as hell don't.
As far as the lineup of 3DS games being good this year, yea it is but thanks to what? One Nintendo IP, and a bunch of 3rd party games that in some cases(DQ) have been out in Japan for freaking years. Very little to do with Nintendo support. Fire Emblem Fates is pretty much it for a big Nintendo release announced on the system in 2016 and they where finished in early 2015...
But Vita will probably have 20+ Japanese 3rd party games release on it this year in the west and 10s more indies, got to love that major support Sony is giving it my dude 3rd party support is irrelevant in this discussion. The DS still got 3rd party support long after Nintendo abandoned it you do realize this yes?