United States
Vet 5 should have never been a thing. Brits Veterancy is extremely potent without 2 extra levels, they just have a lot crammed into 3 which is how OKW should have been designed. Increase the cost of vet by a small amount but cram more bonus's into each level so you have goods scaling in the time from of an average game rather than hoping you drag out into a 1 hour match.
Honestly If I would to point out specific problems I would say it's simply the same reason USF has issues, except we know USF is getting 3 new commanders to help fix this problem and OKW is only getting one.
1. Lack of a effective mainline infantry, now you might say Shrek'd Volks, and well you'd be right the Shrek sure is good but the infantry wielding it are just bad. And with the recent rackten buffs there isn't much to sell Volks on other than he incendiary nade, and then you just need 2 really. I would raise their price up to 250 and make them the middle ground between Riflemen and Grens, also give em a bonus to accuracy/ROF in cover so they won't be blobbed but can still stand up to enemy infantry without falling apart. Currently even Conscripts walk all over Volks until Volks hit vet 5 and now with the Conscript scaling buffs even that won't be the case.
2. Lack of diversity in upgrades and automatic weaponry. Paradoxically OKW has the MOST amount of rifle/kar98k units in the game when the real OKW (well, equivalent anyway) used massive amounts of automatic fire to make up for reduced quality in soldiers and numbers. Almost all OKW units either don't have an upgrade or just have 1 you almost always automatically take. Volks should have at least 2 upgrades to chose from, StG's or LMG34 should be a choice on Obers without a doctrine (IR which ignore cover remaining doctrinal of course), Sturms should have a flamethrower (that locks out the repair one), ect.
3. No real heavy indirect fire outside of the Stuka Zu Fuss. Yeah the Stuka is very effective but it's also horrifyingly expensive which is a non-starter in 1v1 and 2v2. The ease at which you can avoid the rockets has made it relegated to being a building counter which won't be necessary with incendiary nades. Other than countering buildings it's good for countering heavy support weapon play (although you can still avoid the barrages), but still OKW should have some sort of Howitzer commander to give a MP only artillery option.
4. Lack of defensive options. This one is a big hitter since right now OKW's defensive options are limited only to the Flak Truck. The proliferation of indirect fire and the heavy reliance on trucks for OKW has made it so playing defensively like Brits can is basically impossible because if the game drags on to long you will just drown in artillery and off maps. The MG34 can't do it's job; and while it's cheap as chips I would rather have a MG that does it's job instead of just being a piece of shit you can spam. It needs it's old damage back + a little suppression increase and a price raise. The Flak Emplacement needs to not be decrewable and just have it's gun mirrored to that of the Flak Track. A brace type option for OKW trucks (that disabled constructing units and healing/repairing/firing) would also go a long way towards stopping the whole "wait till you can just blow up all his trucks and sweep him off the map" thing.
5. To little fuel and to much MP. The fact OKW cannot spend popcap on high pop cap units (vehicles) means that OKW floats an insane amount of MP because it's never spending it or having to pay the popcap price of having vehicle. A good fix to this would be reducing the cost of OKW vehicles by 20% and increase the MP cost by 50%.
6. To little to late phenomenon. I bring this up because the often "hold out for vehicles" strat OKW is shoe horned into most games simply doesn't pan out unless you hold superior map control to your opponent. A single Panther can't stop an entire armored advance (especially a British one using super high health tanks); a single OKW Panther is worth more than an IS2 due to the fuel penalty but is worse than it's Ostheer counterpart. There is also a snowball effect with the low ROF + high vet requirements meaning getting it up to 2-3-4-5 can take a while because it doesn't deal damage often.
7. Reliance on gimmicks. The reason why OKW remains powerful despite a lot of these things is very powerful gimmicks like going very heavy with Fuss and ignoring T4 by getting a JPIV. Using JLI to essentially replace any other elite infantry. Simply spamming so much infantry you break an opponent because they can't micro faster than you can and get map controlled to death.
Just my take from being a very long time OKW player.
I agree with pretty much everything here. Gimmicky gameplay, poor synergy, weak massy blobs and lack of choices. Even when the OKW performs well they don't feel good. Poor design overall.
And it's so very frustrating spending ~50% more fuel on units that will hardly ever reach high levels of vet. Extra fuel for nothing
Relic Entertainment
cblanco ★ 
Heartless Jäger 
