To what extent would you say that Germany's punishment was psychological rather than physical in the Treaty of Versailles?
I would not agree with this statement to any great extent.
It is somewhat true in that the war guilt clause of the Treaty did not really hurt Germany. You can also say that reducing the size of Germany's armed forces did not really hurt it either--both of these were pretty much psychological punishments.
However, there were some pretty severe "physical" punishments as well. The reparations and the taking of the Saar (or at least its coal) from Germany really hurt a lot. Both of these helped to devastate Germany's economy--that is a truly important "physical" punishment.
So there were both kinds of punishments, but the psychological ones would have been much more bearable if the "physical" ones hadn't been so severe.
The harsh nature of the Treaty, especially in terms of the economic reparations that it required Germany to pay, so damaged their economy and so destabilized Germany that the psychological effects were significant.
Surely, veterans such as Adolf Hitler and other nationalists in Germany felt Versailles was a sellout, and this had an affect on national pride and resentment, but the dismal economic and political conditions Germans lived with throughout most of the 1920s caused more damage. In short, the Treaty caused psychological damage indirectly, while the economic or physical damage was more obvious and direct.