What about a more conventional wank--increasing their effectiveness?
Suppose that Germany decides to begin researching a more advanced medium tank design in 1939 to replace the Panzer IV--so that in Barbarossa, Germany has its own Panzer V; not a Panther, but a much more solid design with the ability to shoot through a B1-Bis' armor.
Japan, having sent advisors to the SCW to study German Tactics, respond to that war by developing their own tank models for their war against China.
The US and UK both invest more in tank technology, because Germany's counterfactual Pz V is more than a match for their own designs.
Inspired by German progress, Italy responds by attempting to make its own variations of the Pz IV and V.
Finally, Stalin, recognizing that war is on the horizon, rushes the T-34s. By the End of the war, the Soviet Union is mass producing T-55s instead.
Basically, everyone invests more in tanks, they all get more benefits from the investment. Silly ideas like the Maus are never developed, and instead, the German "Secret Endgame" tank is something that has major advances in efficiency instead of size; a tank that goes faster and gets better mileage for the same sized engine.
I guess I just don't see the Axis and Allies powers building insane 1,000 ton machines as a real wank.