Anna - Is compared to Impa a lot due to both characters being old time veterans in both of their respective series with recent 'promotions' in their roles. However, unlike Impa, Anna lacks real story importance. She's just a unit comparable to every regular solider. And in terms of abilities, well she'd be pretty much like Robin. But perhaps with Staffs implemented as Specials? I'd be able to reconsider if Anna would get deeper, more meaningful roles as a playable character. She's pretty much a joke character from what I've seen in Awakening, with there still being merchant Anna's and all for example.
The combatative analogy you make against Anna by comparing her to Impa is wholly inadequate, everything that you perceive as lost in story is gained
ad infinitum in every other way, and in that sense it becomes part and particle of the story, in fact, Anna has monstrous impact on every story, I mean, where else are you going to get that steel axe on sale, or how will you interact with the menus and services that Anna hosts without Anna? That's right, you can't! The fact that IS has chosen her as the characterization of various utility necessitates that the utility cannot exist without her, and in fact she becomes the least dispensable character in the whole Fire Emblem universe, what have you got to say to THAT, mister? No, the recent support for Anna is no joke, the recent support for Anna is a sign of its cause, a sign that Anna's level of importance has risen to the point to be weighty enough to contend with Lords, my friend, this weight is the SUM of her roles, most of the weight of which was garnered in the most recent entry, Awakening, where she is by virtue of the one Player Character Anna already on the level of Tharja or Owain or any other minor character. Then, add that to everything else she's ever done and BAM, you got your importance to the series
right there. You make the signature deadly mistake of Anna naysayers, you only consider one Anna, when in fact Anna in Smash would be the representation of a whole, much like Pikachu, and this is one major area Impa
cannot capitalize on, or would by Sakurai in a rather reticent manner, the moveset argument swings wildly from 'lol trickster anna uses a sword' to "Oh ****, we have a real chance here to show off mechanics from Fire Emblem that no one has yet, and other likely choices would not be able to or as likely show these things off as she would, plus a spear user, horray merchant Anna!"