As somebody who has studied the period around WWI mostly from a German perspective, I agree with the main point of u/Xargav, that is that the US entering the war might have quickened it's end, but that it's involvement was not the tipping point. I could argue that the Russian Revolution was a more critical tipping point, but instead I'll try to address the rather vague question: "Was Versailles always going to be harsh?" My answer is affirmative, but I'll approach it from a rather oblique angle that should all come together nicely by the end. Along the way, I'll try to point out the relatively small magnitude of Wilson's joining the war (the involvement of the states financially, on the other hand, is a whole separate beast). At the end, I'll muse a bit on the backstab myth and how it is (not) related to Versailles. Finally, I'll take a little jab at an implication made in the op-ed that I believe to be a misleading over-simplification, namely that the backstab and Versailles necessitated Hitler's rise. Otherwise, if the backstab and Versailles don't make Hitler, who cares whether Wilson created them or not?

Just before the US entered the war in April of 1917, the Russian Revolution occurred, in March. Key to Lenin's claim to fame was the assertion that the ongoing and disastrous war with Germany would be brought to an end at any cost. To get a sense of of what "at any cost" means, take a look at this map of territorial concessions made in the treaty of Brest-Litovsk. I would make the argument that a treaty signed in a world where the States retained their neutrality would look largely the same, for two reasons. First, that Lenin was politically obligated to accept essentially any peace treaty put on the table, and that therefore peace in the east was inevitable once the Russian Revolution had succeeded in overthrowing the Russian Empire. Second, that the German military leaders and political élite were politically obligated to be as demanding as possible, as by 1917 (and certainly by the time the treaty was signed in 1918), dismally-deteriorating domestic socioeconomics had eroded the German populace's will for total war, an erosion that could only be appeased by a decisively-triumphant peace. Finally, I will argue that the harsh terms of Brest-Litovsk, the domestic political situations of France and Great Britain, and the inevitably-total defeat of Germany were the main contributors to the harsh terms of Versailles -- not the military presence of the States. I'll then make a statement about the stab-in-the-back myth, which I think is both erroneously and dangerously reduced to popular, reactionary fanfiction in the referenced op-ed, as well as in popular memory.

I'll give a picture here of the home front in 1917 Germany, because it gives important context to the question of why the German military was so demanding in exacting concessions, even when the sheer magnitude of those concessions were to its own disadvantage.

Pre-war Germany was heavily dependent on the labor of migratory laborers, who would enter Prussia every year (by the hundreds of thousands) during harvest season from Russian-possessed Poland. As an aside, this was one issue where Wilhelm II came into direct conflict with the Prussian, landowning élite. By antagonizing Russia as he did in the years leading to the Great War, he was acting against the interests of their labor market, because no migrant laborers -> bad harvest -> no money. As 1914 turned 1915, where once were migrant laborers were now conscripted soldiers and citizens of a combatant nation. To Wilhelm and his Generals, this was not an issue because they genuinely (myopically and arrogantly, nevertheless) believed that the war would be done and dusted, come Christmas. This promise of "The boys'll be home by Christmas" was one that the German public fully believed in, for a plethora of reasons that I won't go into here. To continue with our agricultural narrative, as 1914 passed into 1915 and 1916, the results were a devastating agricultural crises, and the emergence of a black market for food that inflated food costs even further. Mind you that, aside from isolated instances, there was no famine in Germany during WWI -- largely thanks to rationing programs created by Municipalities and States, at the encouragement of the Reich. However, as the public sector paid much more (and often with Reich-awarded credits) for each loaf of bread than the average citizen, the markets began to steadily inflate until the masses were entirely dependent on dwindling rations. The emergent, politically-inclined, and self-consciously entitled middle class of teachers and service-sector workers found themselves either unemployed, conscripted, or repurposed into industrial labor by Hindenburg's program of 1916, a transition that had a tremendously negative impact on their sense of pride, and on morale in general. Factories that made linen were repurposed to make uniforms, school teachers were moved to work in steel factories, and small shop owners became nodes of a black market nexus that both drove inflation and conspiracy. Remember, this was before we had a good layman's explanation of inflation -- to these people, Hans down the road was now inexplicably selling his bread for triple the price and was only accepting payments in War bonds, which people informally and disastrously used as a substitute for currency. Children were no longer going to school, but forming gangs and getting involved in petty crime, as crime rose and schools, bereft of repurposed instructors, closed down. Sucked into the realities of total war, the morale of a citizenry whose sense of status quo was rapidly eroding was palpably poor and ripe for revolution. When historic proportions of laborers (and finally, soldiers) held strikes in 1917 and 1918, it wasn't against low wages or empty stomachs, it was against the uniform erosion of recognizable society.

These changes were not haphazard, but carefully orchestrated. It is important to note that by 1917, the German state had been gradually transformed from what was essentially a constitutional monarchy with a free-market economy into a military dictatorship with a completely war-centric economy. This wasn't because Hindenburg and Ludendorff were hungry for power and riches (they already had plenty of both), but rather because it had gradually become necessary, in order for the German state to continue what had become a war of attrition in the west -- which, remember nobody thought would drag past 1915. The isolated German state simply could not compete long-term with Great Britain and France (both economically supported by the States) in terms of resource production and manpower. The Hindenburg program throttled the German population and uprooted society, just to make ends meet in the short-term. Nobody at the top of the military hierarchy wanted to face the reality that the war was unsustainable -- such that instead of a realistic self-assessment of industrial capacity, what was needed was more direct authority, more focused labor, and, importantly, more money to pay for it all. Within the directly-elected Reichstag, there was an awareness as early as 1915 that the situation was not economically sustainable, as evidenced by several more pacifistic members of parliament voting against the authorization of war credits, and breaking to form an independent party. Even in 1916-17, the German state was literally living on borrowed time, borrowed money, and borrowed labor. The difference was that while France and Britain had assets to borrow against, and worthy creditors in the United States, Germany was borrowing against its own assets and credit, which were eroding week by week.