Were the Allies too soft or too harsh on Germany in the peace treaty at the end of WWI?
I would argue that they were too harsh on Germany. This was particularly true of the war guilt clause of the treaty and the reparations demanded.
The Treaty of Versailles essentially demanded that the Germans acknowledge that the war was all their fault and pay for its damages accordingly. This, from an objective point of view, was unreasonable. The war was by no means all Germany's fault. The idea that Germany should pay for all the damage caused by the war was ridiculous. But the French and British wanted reparations, in part to be able to pay their debts to the US.
These two clauses, when added to those that did such things as stripping Germany of the right to have an army, were excessively harsh. They condemned the German economy to weakness and they ensured that Germans would remain angry. This led to WWII.
When we compare this treatment with the much more lenient treatment afforded Germany and Japan after WWII, we can see that the Treaty of Versailles was too harsh and was, therefore, counterproductive.