Watching cutscenes is playing the game. I've never understood this complaint as, this is a final fantasy game.

Yeah the start is slow, but it's just setting the stage. You're only past the first dungeon.

Shadowbringers had a more intense start because, as you said, we're thrown into a completely foreign world/dimension coupled with the mystery and urgency of finding your missing friends.

Endwalker is slower because everyone is safe at the start and there is no immediate peril.

Why assume the entire expansion will be slow after playing a few hours? That just seems kinda silly to me, especially if you've seen the trailers.