I wonder if the difference is local detection vs cloud? For G4, Face Detection does not require a home guardian subscription, but for G400 it does.
Based on previous comments from the Aqara team it might be due to hardware limitations (N.B. G400 is not specifically mentioned, just following the principle).
So 1) there’s going to be more latency by default and 2) if its extreme we should look at your network and anything that might be slowing down those connections. Then if there’s nothing local introducing the latency it could be on Aqara’s end.
Hoping Aqara’s team can comment. on that. Have you opened a support ticket?