For someone who likes their games to be large in scope (especially Pokemon), I found the lack of a National Dex a bit disappointing.
It's one thing to acquire the National Dex late in the game (e.g. post Elite Four), since you will most likely not be too concerned in completing the Pokedex until after you beat the Elite Four & having access to battle facilities. It's whole other matter when you eliminate it all together, and slot it as merely another feature in an application that exist outside the games.
One could make the argument by moving the National Dex into the PokeBank, this solidifies the PokeBank is a feature for all Pokemon games across the board that have access to the app, and removes a certain barrier of entry from completing the National Dex via exclusive Event Pokemon.
However, I think this sets a precedent that each of the games are not as strong (single-player) entries of each series, and merely an extension of the PokeBank. Also, I could be sympathetic to an argument that proposes that achieving all entries of a PokeDex in a game to not be as rewarding with a National Dex present.
For myself, I see achieving the National Dex as more a secondary factor in the games---a bonus, if you will. Nonetheless, I am still not a fan of having this feature removed, as I see the idea of having a (National) PokeDex to be a core feature of the series.