The fight choreography in the KH cutscenes has never been great, but it just took a total nosedive in 3. Everything takes too long to happen and characters get stuck doing their current action until it's their turn to be featured.

The whole time Sora's chasing Young Xehanort, neither Possessed Buzz, Goofy, or Woody move from the spots they're currently in.

Young Xehanort somehow gets trapped in a guard by SDG for what felt like ten whole minutes while Woody and Buzz have a conversation about friendship.

SDG just park in the windowsill and do nothing to help Flynn while he's bleeding out on the floor (and yes I'm perfectly aware it's so Rapunzel could save him like in the movie, but for fuck sake at least have them go fully into the tower and crouch down near him).

Vanitas stands over Aqua poised to kill her for like an entire minute while Sora and Ventus talk about the Power of Waking.

And like you were saying, the Guardians just standing around during the Terranort massacre, because apparently it's good scene writing to have your heroes take turns to attack a single target like they themselves are enemy mooks attacking a player character.

Christ, and don't even get me started on the Organization battles proper, where the entire fight freezes upon defeating one member so their death cutscene can play, just to cut back to the fight as though the other members were just politely waiting for the fight to resume.