Originally Posted by
Zairava
Flavor, style, impact.
It makes it feel better to press and unique compared to every other melee and that's why people enjoy it. It doesn't need to be magical for it to have a cast time, I find that to be incredibly restrictive.
Without the cast time it just feels like any ordinary GCD, with the cast time it feels like something unique that's a part of what makes Samurai what it is. I feel like Tsubame Gaeshi would lose its luster as well, as that is the instant cast and it feels better since the only method of doing so is casting an iaijutsu to begin with.