How does it even matter that Kizaru was just immobile for a moment or not? It is a fact that Star Gun damaged Kizaru enough to put him in such a state, regardless of whether he gets up after 6 minutes or 1h. It is what it is.
If there is a second round, Kizaru might still show far more but for now, he simply took an L. It's no shame considering it's ACoC + G5 named technique. Not every top tier is like Big Mom or even Kaido in terms of endurance and durability.