Just finished watching.  I thought they were reaching, a bit, on their talk of Jack's monster comics and the war. and they lack context on the Demon; but, there was a definite influence on the 4th World and, especially, The Losers, which I brought up in my Kirby review thread.  Jack hated Sgt Fury, because it was a fantasy of the war and got off it as quickly as he could.  The Losers better reflects his war, with close quarters fighting, artillery barrages, tanks, mud, cold and desperate battles.

Jack fought in the Lorraine Campaign, Patton's push to take Metz and push into the Saar; but, he lacked the supplies, especially in September, 1944, as priority had been diverted to Montgomery and Operation Market Garden, the attempt to seize the Rhine crossing, at Arnhem, in The Netherlands.  That operation failed and Montgomery ended up bogged down in Belgium and Holland, while Patton had to relocate to Luxembourg, before the German offensive in the Ardennes set off the Battle of the Bulge.

There are some clips on Youtube, of Jack talking about the war and a fight inside a factory, which illustrate how desperate the fighting was, in his sector.  Patton ended up taking a lot of criticism for how he executed the Lorraine Campaign and the casualties suffered, while their opposition was not exactly the cream of the German Army or Waffen SS.  However, the German's fought hard at their frontier and were experts in deploying their men in fighting positions and fighting rear guard actions.

I just finished Antony Beevor's D-Day, The Battle of Normandy, which covers the entire Normandy campaign, from the D-Day landings, to the eventual breakout, the Falaise Pocket and the liberation of Paris.  Normandy suffered greatly from the fighting, with whole villages levelled and heavy German reprisals for Resistance activities and aid to the Allied advance.  You don't get a lot of that suffering in most histories of the war.  Once the Allies break out, they move swiftly across France, and the Operation Dragoon landing, in the South of France, also moved rapidly and it was felt that the easier liberations of the rest of France owed to the suffering that Normandy faced, as it helped break the back of German forces, in France, greatly depleting their armored formations.

By the time Kirby is arriving in France, that phase is mostly over, as Paris was liberated by August 25.  He arrived in time for the long, slow push into Germany.

The argument has been made for Kirby (I'd throw Ditko in the mix) needing someone else to give his work a more commercial outlook. But Lee just was at the one at right place and time. We all would've benefited as readers, had someone with better writing skills been there instead.

What Jack wanted more than anything was to be left alone to create his comics with minimal interference. To that extent, he quite liked have Stan as an editor. Before he left Marvel in 1970, he was starting to work on his own stories. IIRC he did Ka-Zar and Inhumans stories. It's possible that if he'd stayed at Marvel he would have been given the freedom to work on his own books. I also think it's highly possible that he could have been given the art director role and secured a permanent role at Marvel. Kirby wasn't particularly happy with Marvel's new owners, IIRC, but I'm sure something could have been worked out. 

Commond, I think by that time, Kirby had already moved to California, and I don't think he had any desire to be an art director. But I do believe he was developing the New Gods for Marvel.
If I can find the specifics, I'll post it. But basically, rather than negotiate a new contract in terms of royalties and guaranteed pages, the new company sent him a letter to sign saying he has no rights and he must sign it to get any work. He walked.

Though at times he could lay it on just too thick. His Silver Surfer being an example. People say Kirby failed without Stan. Though the reality behind the cancellation of the Fourth World is more complex than "it didn't sell". It sold better than other books that were not cancelled.
But Stan's big book launch which he did without Kirby was The Silver Surfer. It also failed. As a teen I loved that book, and the Buscema art is still some of his best. But the quality of the book , as many keep saying in regards to the Fourth World, doesn't seem to be relevant when people want to criticize what Kirby did without Stan.

I would very much like to read the story where Kirby does ragnarok in the Marvel universe and the New Gods/Eternals whatever come after.