I get your point, after all if he is the gatekeeper of the gate beyond the first zone, then he must be inside the zone constantly.
But the gatekeeper isn't really Kuroko, but probably a partner or a teammate they trust the most.
And that's why for Kagami and Aomine, it was Kuroko, their shadow.
But Midorima or Murasakibara probably wouldn't see Kuroko, maybe Takao or Himuro would be there instead.
I think the keepers is actually their best partner who could judge whether they are ready to do a real team play while in zone.
It just happened that for Kagami, it was Kuroko.
Maybe spoiler idk
Is it true that kuroko is the zone its self??? That kuroko has always in the zone
Ive read comment about it but idk if its true or not or if it just some opinion