To keep it simple, let's assume 200 cells in both systems. In the 400V case, you have 2 parallel chains of 100 cells in series, and in the 800V case you have a single serial chain of 200 cells. And let's assume you are trying to get 200kW into the battery. This implies 500A in the 400V case, and 250A in the 800V case.
However, in the 400V case the current splits between the two parallel chains, resulting in 250A through each chain.
In other words, it's basically equivalent to the 800V case.
So no, I don't think there is any inherent advantage to the 800V architecture in that respect.
This mirrors my understanding.
As for 800v before the pack, I gather that boils down to two things:
Money: more copper in 400v systems, more expensive electronics for 800v. For now, 400v wins
Charging cable: lower currents mean longer, lighter, and less clumsy. Water cooled 400v cables has brought the comparison closer, for up to 250 kW.
It is true that the 800v cabling will have less heat losses but I don't think the difference carries the day.