Female might have mattered, maybe, back in the days when we had the Brawl roster with barely any female characters. Now, many females were added, most of whom were completely random choices and didn't make it on their own merits. While Dixie was the biggest one who could've made it as a legitimate female, she missed the boat for getting on entirely for marking a political correctness box. Despite the lead villains had in Brawl, females are now a decent chunk ahead of them.
Whether or not you think "villain" is something silly to put up on a pedestal with "female" due to not being politically correct, the Smash fanbase very obviously has a high demand for villains with Ridley, Mewtwo, and, yes, K. Rool. The lack of these characters (at one point in time in Mewtwo's case) was the source of most negative reactions on the roster. Whether or not the ballot is a "suggestion box", it wasn't made for absolutely no reason. Many, many advertisement characters have already been added, and if it was actually of remote importance to add Dixie to advertise Tropical Freeze there was -plenty- of room for a Donkey Kong character in the initial game with a lot of the weird roster choices.
Adding more female characters has absolutely
nothing to do with "political correctness". Adding more female characters has more something to do with the fact that female gamers want characters they can identify with when picking them. I've played plenty of times with female players before - my sister, just generally female friends or the girlfriends, sisters or even mothers of people I am befriended with. Most of them gravitate towards either Kirby or, more often, female characters. I've seen my sister play most often with Zelda, while the girlfriend of one buddy of mine loves playing as the female Robin. His mom enjoys playing Wii Fit Trainer, and always picks the one with the yellow shirt.
And while Smash 4 added a big chunk of female characters, I'd still argue that it wouldn't hurt to have more female representation.
I understand the villain argument. Really, I do. I've been heavily pushing for Ridley and Captain Syrup, personally - just ask any of the SmashGAF regulars. And I've also been hoping very much for Samurai Goroh or some other F-Zero villain. But villains aren't a group of real life people that would like more characters they can identify with.
Either way, I don't see how the new female characters are "random choices" that were "only picked cause they are girls". I'm sure that adding female representation was something Sakurai wanted to pursue, but it certainly is not something that he is putting an emphasis on.
I don't think I really need to argue for the merit of including Villager. But: Him, Robin and Jr. were predominantly presented as male characters in promotional material, and their main selection is male.
After the main 4, Rosalina is one of the most natural additions to Smash for the Mario franchise. She's getting pushed to be adopted into the "main family" of Mario characters, is incredibly popular with the fanbase, and also represents modern Mario, while Bowser Jr. is more representative of the "New" Mario Bros. series - Wendy barely, if at all, counts as a female addition imo.
Palutena has been a main character in the last game Sakurai created. She was already a support character in previous Kid Icarus games, and got a massive revival due to Uprising and her redesign, as well as her appearance in Brawl, as Pit's Final Smash. The new game also was pretty damn popular, especially in Japan.
Robin is not only a unique addition to the game (due to his sword/magic style), but he also is the player avatar from the most recent Fire Emblem game, and pretty much akin to Marth, Roy or Ike for their respective games. Additionally, he represents a whole new concept for the series (as players never were able to create an avatar before Robin). As mentioned, however, Robin is defaulted to male. Lucina is more a coincidental addition than a planned one; she originally was supposed to be a alt costume for Marth, but ended up with her own spot on the roster because Sakurai had some leftover development time and decided to beef up the selection. And even though Lucina is a clone, she at least gives more representation to female characters.
Lastly, Wii Fit Trainer has been the fourth main female character in promotional material, although half of her alts are male. And even though people say "Yeah, well, she's one of Sakurai's wacky things to troll us", and even disregarding the sales argument, the Wii Fit Trainer character is very recognizable, believe it or not. With the massive success of the Wii last generation, and the massive success of Wii Fit, many many people can see the Wii Fit Trainer and recognize her as such. Furthermore, she fits the mold as a Smash Bros. character so well that I don't understand why people still argue her inclusion is random and without merit.