The only reason Spirits would deconfirm a character is the lore behind it (Spirits are the actually energies of characters who were destroyed by Galleom and lost their physical form), but seeing how we now have a spirit of Kirby with the Star Rod, it's pretty clear that was just an excuse plot to justify spirits.
On another note, I thought of a reveal trailer for Lycanroc:
-Smash intro screen
-The scene takes place in a canyon
-Greninja and Lucario are running towards an opponent, revealed to be Incineroar
-Greninja jumps and attempts a dive kick, Incineroar side-steps this attack, grabbing Greninja by the foot and throwing him off-screen.
-Lucario steps in and uses Force Palm. Incineroar ducks under this, lifts Lucario horizontally over his head, and preforms a back-breaker on him.
-This attacks sends a shock-wave, which rustles the trees in a nearby forest, awakening a canine figure.
-Proud of his victory, Incineroar begins his signature pose-off, flexing his muscles and growling. Behind him, a bunch of sharp stones slowly begin rising one-by-one.
-He turns around with open arms, ready to take in any adoration from the audience. He gains a surprised expression when he sees all the floating rocks.
-The floating rocks begin flying towards him, as the screen cuts to black with blue impact sparks where Incineroar was (think of Akuma's Raging Demon from Street Fighter)
-Incineroar is knocked out on the floor, as the back of an orange figure lands near him. The camera pans around him to reveal its Lycanroc, who lets out a howl.
-"Lycanroc gains his edge!" splash screen
-Cue gameplay of Lycanroc and his stage, culminating in Splintered Stormshards.
-After this, the trailer cuts back to CG, where Lycanroc is cautiously retreating from and growling at Lucario and Greninja's spirits.
-A paw lands on Lycanroc's back, with the camera panning up to see Incineroar
-He gives Lycanroc a cocky yet respectful smile, confirming their alliances
-Lycanroc and Incineroar run to clash with Lucario and Greninja, with the screen slowly fading to black.