Early game: Kubel. This guy requires a lot of care, and will likely die to schrecks anyway, but early on he can put you in a good position.
Mid game: Flak halftrack. This thing when used properly is a complete beast. This is honestly one of the strongest counters to infantry blobs as long as you keep him repaired and be ready to screen an escape with some smoke.
Late game blobs you really need artillery to contend with, which is fine because OKW has it in spades.
The Kubelwagon is a piece of junk that dies to infantry even if you spend all of your time microing it to keep it out of enemy fire since one rifleman squad can shoot it half to death before it starts suppressing them.
The flaktrack is defeated by 2 to 3 bazookas or even BARs. It's a piece of tissue paper overall. Hell, it's even defeated by minor changes in elevation which cause it to completely miss the target and fail to suppress. I love this unit as well, but it definitely isn't even a early game counter to blobs.
And on late game, the damage done by the blobs is usually done by this point, and spending hundreds of fuel on artillery units cements your fate since you'll no longer have any left over for the tanks you were supposed to be saving up for all game long.