Spirits are such a great concept to me because they allow many more characters to be represented than before. They are superior to Trophies because 1) they aren't exclusive to characters with ingame roles or existing models; 2) they serve a gameplay pirpose so you feel like you're using your faves instead of just having some toy collecting dust somewhere; and most importantly 3) Spirit Battles show an incredible level of care to these characters and their lore.
Sure, it's not perfect, but representation is never 1:1: all the status effects, stages they take place on, character and costume they possess, music that plays, etc. shows the dev team CARED enough about these characters to referemce them with these fun little battles.
And also, this is how you take the concept of this being a kid playing with toys to its extreme, you give the child imagination.
This kid may not have a Sigma toy, but they can pretend this Ganondorf they do have is him.
I remember pretending toys I had were things other than they actually were, it's not such an alien concept to play pretend and, honestly, I love it. In a way, it ends up feeling nostalgic.
Ganondorf/Ganon is the same person across all games(except for FSA where that's Ganondorf II) just with different designs. Which is why a DLC fighter with an existing Spirit just needs a different artworl for their Fighter Spirit and blam.
I mean, when you have **** like this
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I find it hard to take the argument that it wouldn't make sense for a fighter to equip their own Spirit seriously.
"Oh but it's KAPTAIN K.Rool, not KING K.Rool"
Well yeah, that ain't gonna be Geno equipping Geno either, it's gonna be Geno equipping his brither, "slightly looking left" Geno