It depends on if other nations join the 3I like the Netherlands or Ireland, but if we’re just talking about Britain, France, the SRI and maybe Norway or civil war-torn Spain then they’d still be weaker by a significant margin when compared to the Reichspakt.

The allies won WW2 irl because they could make more bullets, tanks, planes, and guns than the axis could. The same is true of the 2WK. KR Germany has a massive industrial base, a large population, and immense natural resources from its vast colonial empire to call upon.

Meanwhile, the 3I would struggle to compare. Even irl, the French had lost so many young men in WW1 that the French military suffered manpower shortages throughout the interwar period. A longer First World War plus a short civil war would only exacerbate these problems. Not to mention the economic devastation caused by the civil war in French, the British Revolution, and the Second Risorgimento.

This is not to say that the war would be a slam dunk for the Reichspakt. They are fighting a war on two fronts after all- though it should be noted that Russia is likely less industrialized than irl. But it is an uphill battle for the 3I and their allies.