What Primis Richtofen picked up from the body was not the "radio" from Ultimis Richtofen's uniform, so he could communicate with Groph in Der Eisendrache?
But I think this conflicts with the idea that the Zombie Richtofen from the comics is from the body of The Giant, since you can see that he still has the radio.
Unless it's Treyarch's mistake, but knowing how careful they are with details may not be the case.
Also other points I would like to point out about The Giant are two initial quotes from Primis Richtofen in solo.
These seem to be related to initial quotes from Revelations and Blood of The Dead.
In Revelations the quote says:
"Mein gott, what have I done? Stop it, Edward, breathe, it's okay... MAXIS!"
This is after Maxis got trapped in the Summoning Key and the Shadow Man escaped.
In Blood of The Dead says the following:
“Maxis! Stop it Edward, this may be just another delusion. It must be. Surely, I would never lead myself in such a..., such a...? Mein gott!, Everything could change!"
And in the intro after Brutus closes the portal it says:
"Mein gott. What have you... What have i done?"
The first is after the Kronorium changed and the Primis Richtofen got caught in Alacatraz.
And in The Giant the quotes says:
“Maxis! No wait, compose yourself Edward. Mission accomplished.Temporal disruption achieved, the future is changed.”
“Mein gott, what have I done? Stop it Edward, breathe, it’s okay, it’s okay. This is important, this is what you have to do, even if another part of you dies each and every time. AGH! How am I meant to work when all around me, I am beset by the voices of the damned, and the doomed!”
Now, in Revelations and Blood it makes sense because they are after shocking moments, but in The Giant it does not make sense that Primis Richtofen is distressed.
The quote comes after he kills himself in the opening scene, but it doesn't seem to affect Richtofen because of the quote "When I died I felt nothing".
So, could it be a possibility that this line parallels Blood of The Dead, with this Primis Richtofen being the one who delivers the Kronorium in the opening scene and goes through the portal? If that makes sense.
Or it could also be that he's distressed by the "fractures through space-time" that the timeline says are created after he kills himself.