Tiger IIs were deployed on the Eastern Front in September 1944, so it still fits the Ostheer perfectly fine. It isn't more of a stretch than giving the Brits the Comet or OKW the MG-34.
I agree with you, for the most part, however still the WFA are centered largely around the Battle of the Bulge, while the Brits are based around their Rhine crossing Army in 1945, which perhaps makes sense with the lack of the 25 pounder emplacements and their less reliance on emplacements to some extent.
I actually went as far as to have the idea of replacing the Wehrmacht base buildings with the OKW HQ trucks since it made more sense, the Ostheer part of the Wehrmacht was lightly armed and armored during Operation Barbarossa and highly mobile, as well as well trained and equipped, supplied and had a lot of available manpower.
To that end I'm not going to go into much detail but this is how the Ostheer would look like in my mod if I made it:
HQ truck (T0)
Combat Pioneers - 5 man squad armed with MP40s, could be upgraded to flammwerfer 35s and Panzerbusche 39s exclusively. Could also plant demo charges to destroy cover and so forth, build sandbags, Tank Traps and Bunkers of course. Can't repair vehicles, only structures.
Grenadiers - 5 man squad using the AT crew models armed with K98k-s, could be upgraded to MP40s or an MG34, access to rifle grenades at first, gets replaced by regular Stick grenades when upgraded, can stack sandbags.
Kubelwagen - comes unarmed and can cap, can be upgraded to an MG34 but loses the ability to cap then.
The HQ could also be upgraded with medics.
Infantry Support HQ truck (T1)
MG34, GrW 34 and Pak 36(renamed M42, but can garrison due to small size, was on the fence about giving it a retreat like the raketen).
Mechanized Panzer HQ truck (T2)
Panzergrenadiers - 5 man squad armed with Kar 98k-s same as the regular grens, could be upgraded to Mkb 42s (renamed StG-s) or an MG34 again like the Grens and also perhaps to Panzerbusche 39s? Can only repair vehicles and throw bundled grenades.
251 Halftrack - Open Topped, when infantry are inside the MG34s on it are manned, can be upgraded to a mobile ambulance (can be setup to deploy medics and reinforce infantry, perhaps could even have a forward retreat point?), mobile repair shop (same as the ambulance but instead of medics it deploys repair pioneers) double flammwerfer 35s on each side and doctrinally can be upgraded to the Walking stuka and perhaps others.
250 Halftrack - comes unarmed, can be upgraded with an MG34 or a GrW 34 mortar. It can also carry a single squad, serves more as a light and faster support HT compared to the 251. It would be nice if we could put a Panzerbusche 39 on it but I sadly think it's impossible atm due to no model editing.
Panzer support HQ truck - (T3)
StuG III E - Short barrel StuG, nuff said.
Panzer IV F1 - Short barrel Panzer IV, found in Theater of War missions, same as the StuG. Would be nice if we had a Panzer III as well...
Schwerer Panzer production upgrade - (serves as a pseudo T4)
Upgrades both the StuG and Panzer IV to their long barrel versions, allows the calling in of a Command Panzer IV, said Command Panzer IV can be upgraded to a long barrel version but has a lower rate of fire and accuracy due to additional radios. Also unlocks the Panther.
Bunkers can only be upgraded to MG34s, that means that healing will come from the HQ or mobile ambulance HTs, repairs are divided by Combat Pioneers and Panzergrenadiers, repair pioneers can repair both buildings and vehicles in their immediate vicinity. I am also still wondering where to put a forward retreat point, in the infantry support HQ or in the ambulance.
This redesign of the Army is meant to replicate the early to mid war Ostheer, like I said, mobile, well trained and equipped (not best) and having a lot of manpower available to them, that's the reason why for the 5 man squads.
It also has an interesting dynamic where you could go pure infantry without the need of tanks so it's entirely up to the player and how the match goes.
As far as the OKW goes, they would get the wooden base structures, heavier and later war stuff like the MG42s, Pak 40s, Panzerschrecks, Stg-s (proper assault rigles compared to the Mkb 42s) side skirted Panzer IVs, Jagdpanzer IVs, Panthers by default, concrete bunkers, dragon teeth tank traps, Pak 43s, King and Jagdtigers and so forth.
Of course the Ostheer would also have access to heavier stuff like the Tiger, Pak 43s and Elefants, MG42s, Pak 40s and Panzerschrecks but doctrinally.
The OKW would however be a slower to develop and heavier more defensive Army like the CoH Wehrmacht than the current early game rush Axis force they are right now, they would also have more 4 man squads because of the lack of firepower and more experience.
So it would basically be a trade off between the 2 German Armies in my mind, the Ostheer becomes this early to mid war rush Army that is mobile and light and the other things like I said while the OKW becomes this slow and "fragile" behemoth that has access to less manpower and resources but more experience and better weaponry.
So to get back to the topic, I would cut Ostheer to 1943 in terms of tech and the OKW would take off from there until the end of the war basically.
Still tho, I mean your suggestion is nice and all but I'm gonna go with the "unique" crowd this time (god forbid) and say that the KT just simply doesn't fit with the Ostheer's time frame so to speak.
And yes the Soviets would be redesigned as well like the Ostheer in an early defensive Army again focusing on the early to mid war period and I guess most of their stuff would not be weird since they didn't really "tech up" during the war compared to everyone else so to speak, no rocket propelled anti-tank weaponry, no Halftracks of their own and so forth.