Dixie has in fact appeared more than K. Rool and also represented the mainstream Donkey Kong series outside it's own series in games such as Mario Sports, Diddy Kong Racing, and almost Brawl (yes I know she was supposedly a duo mechanic, but you can still play as her like you can play as Nana).
Oh yes, Dixie has ONE more appearance than K. Rool. Which is all thanks to the Mario spin-off titles. You're overplaying that a bit too much for just one additional appearance, don't you think? After all, K. Rool pretty much been the main villain for most of the Donkey Kong games (not including Konga, Returns, and Tropical Freeze [to our knowledge]). So with that in mind, Dixie is still fairly insignificant to the franchise as a whole when you compare her to the main antagonist. It isn't like she has Zelda or Peach status, she's just another sidekick that tags along. She isn't nearly as important as everyone makes her out to be, but Dixie still fits as a fourth playable character. K. Rool would still be the best choice for a third one, due to his role as the overarching antagonist.
Most wouldn't consider being playable in a game series more to be a plus, but in the case that it rivals a character's importance I would count this.
So then, you're suggesting a secondary sidekick is more important than the overarching villain of the franchise?
Not to mention Dixie Kong starred in her very own game. She seems to be very popular in Japan as well and Kongs just seem like the more preffered characters in the Donkey Kong Country series. Granted King K. Rool not being a Kong would bring diversity, but still. Even if K. Rool is the villian, she's just as iconic to the series if not slightly more.
Yes she stared in her own game, with K. Rool remaining as the main villain. She then didn't appear in the following game that had three new characters replace her, but it still had K. Rool as the main villain.
Your reasoning for Dixie being more important to the Donkey Kong franchise as a whole is poorly constructed, she isn't a main heroine, she's a sidekick's sidekick primarily. Being playable doesn't suggest that a character is overwhelmingly important.
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PS: Lysandre is best Pokemon villain.
I don't like Lysandre all that much, Cyrus / Giovanni / N (Even though not really villain) will always remain on top to me.
[collapse="lel xy spoilers"]Lysandre's intentions weren't really all the interesting, "wow i hate the world cause its not pretty so ill just kill everybody waah"
It doesn't help that it all could have been avoided if Sycamore just spoke to Lysandre for like 5 minutes about it.
AZ is like my fav char of this gen tho, but I just think the way they introduced him was really weird. But I did like his backstory a bit, pretty well thought out (even though I feel that he could have had a much more impact on the actual plot than just showing up at one point to confirm his existence).
Also Looker quickly became like my favorite Pokémon character like ever and he barely does anything in x and y[/collapse]