Personally, they look very similar to me.
I understand that. FS took their “creative liberties” and made them look almost like pallet changes.
And they are supposed to he relatively close, considering that Kriegers are inspkred by WW 1 Germans and Steel Legion is inspired by WW 2 Germans (in military tactics and somewhat in aesthetics only).
That’s because GW re used the general theme for Krieg, they just swapped their helmets and coat colors. Very successful instance of re purposing older stuff in a newer release - GW introduced Krieg as a premium version of normal 40k armies, with a price tag that has always followed suit. And their own lore that has since been cringed into them apparently being suicidal mostly child soldiers instead of disciplined troops that are used to surviving on the worst environmental conditions the guard encounters. Hence their protective rebreathers.
But Steel Legion are the OGs and easily the most awesome guard regiment ever.
You ain’t really wrong. They do have some similarities.
Your truth)
A helmet with a visor is so good
They must’ve needed them for the Xbox players 
But we aren’t - as they are Steel legion - not death Korps. Two cool Regiments with very different lore.
From two completely different systems too
Loving that first image.
Still waiting on that friggin’ Long-las FS.
It would be safer to say that they are Western Front as there are also British elements in the aesthetic. The chest bag for the DKoK rebreather is where the British soldiers wore their respirator bags, and the DKoK Engineer armour is rather similar to a type intended for use by Royal Engineers.
Sorry to be that guy, but the DKoK appear in the back of the '99 Guard codex as concept art page of regiments, along with Steel Legion (going from memory for the latter). They were concept contemporaries. GW, when creating the famous regiments must have had loads of concepts for regiments in line with their drawing on history for the Guard. The original famous regiments were drawn out of a particular side in a conflict or as an amalgamation of uniforms from multiple sides in a conflict, or as a basis from a cultural aesthetic. Valhallan = WW2 Russians, Mordian Iron Guard = French and Prussians from Franco-Prussian war, and so on.
Regarding their “cringe” background, it draws on historical fact. It is well documented that during the Great War, on Allied and Axis sides, child soldiers existed, and joined up whilst lying about their age (with recruiters turning a blind eye), or, in the case of Germany towards the end of the war, their ranks increasingly contained teenagers to make up for the shortfall in numbers. Furthermore that desparation to die for the God-Emperor comes from the fanatical desire that was prevalent during the Great War. For British soldiers the fear was that they were the last line of defence against an invasion of Britain, so they had to stop the German forces on the continent to protect their country, family and home. For the French it was their home under attack and they needed to stop the Germans and wipe away the shame of the Franco-Prussian war. The entirety of the conflict saw incredible discipline (British army only had 1 mutiny for the entire war, at Etaples in 1917 whilst the French had multiple) despite the horrors and courage beyond belief. All of those themes are combined for the Death Korps.
Like everything GW created with regard to the Guard and the Imperium it is all built off of our human history. The Imperium is a collection of the absolute worst parts of human societies, whilst the Guard is human military history re-packaged for their space fantasy setting.
I’ll post that page when I can later today.
EDIT: The pages from the '99 Guard Codex do not contain Steel Legion, but you can see the Death Korps third row, fifth from the left. As Steel Legion were released in 2000, they would undoubtedly have been in the concept stage when that Codex was printed, so who knows why they were left out?
until you realise the forward facing shoulder armour would obscure your aiming, since our veteran is right-handed.
Also, they need to stop adding one pauldron, one piece of leg armour, bullets on my hat, and all these small little decorations. They don’t add to the armour, they detract.
Powerful)
It also exists in cadian green but not in the Kasrkin camo