Yeah, what does tomboy even really imply anyway? I always just thought of Daisy as loud and energetic.
http://tvtropes.org/pmwiki/pmwiki.php/Main/Tomboy
"A tomboy is a girl who has tastes and behaviors usually associated with boys. Because these associations are culture-dependent and tend to change, what exactly constitutes a "Tomboy" is subjective. Especially historically, any girl interested in science, mechanics, sport, or combat has been called tomboyish."
Basically, it's vague, as exemplified by the numerous sub-tropes. But if we take the "girl who acts in a way or likes things traditionally associated with boys", then Daisy doesn't even come close.
And if someone wants to argue about how she "plays sports" then every female Mario character is a tomboy.
Link or Olimar's inability to jump aren't integral parts of their design, nor do they have an actual reason for not being able to do outside of gameplay (Captain Toad's being his heavy backpack prevents him from jumping).
Those are integral parts of their gameplay too though, the game wouldn't work if they could jump at the player's will.
Still, the "X thing is integral to character but they can't work as a fighter because of it" argument is stupid. Smash characters aren't 1:1 of their original counterparts, they are adaptations so they can fit in a fighting game, something I believe Sakurai realised when he went back on his word about Villager.
"Should this character who, by all merits, should be in the game, be excluded simply because it wouldn't make sense within canon?"
Sonic can't swim in his games and that's a vital part of gameplay, yet he can swim in Smash; Bayonetta becomes nude when using some of her attacks in her games but she was changed to fit her into Smash; Kirby can infinitely jump in his games but he was given a limit to make him a balanced fighter; Pokemon can only have 4 moves at a time yet Pikachu has 5, Charizard has 6 and Greinja has 5/6.
I could go on and on but I think you get my point.
Tl;dr a character's limitations in-canon has never stopped anyone from being made into a playable fighter
Overtly energetic when competing in athletics - Her reactions in Mario Strikers series. Pretty common among tomboys.
Punches Bowser (not slaps, punches) in mario party 3... pretty tomboyish.
And she’s being judged as a tomboy as an English translation of a culture that sees any woman acting less demure than Peach or Hinata from Naruto as tomboyish. Which makes most the females in the Nintendo canon except for Peach and Isabelle tomboys.
Energetic isn't a tomboyish trope, Genki Girl is a thing. Also, tomboyish=/=competitive
Guess Sumia is a tomboy then, look at that punch she gave Chrom!
If you're gonna use the "Japanese culture" argument, then you should know tomboys are very explicit in Japanese media, like, they'll have short hair, use clothing associated with men and so forth.
Next you're gonna tell me Samus is a tomboy.
Also, by your argument, at least 90% of Nintendo's female characters are tomboys so then Daisy has nothing special for herself ¯\_(ツ)_/ ¯