How can a boost PFC (Vienna rectifier) lower the voltage?
The point of a Vienna rectifier is it integrates both active rectification and boost topology.  In your simulation, you ignore the 2 crucial components: the inductor and back-to-back FETs. When the \$\left|\frac{dV}{dt}\right|\rightarrow0\$, the inductor is sourcing current. This continuity of current allows the capacitors to be charged up further, resulting in a higher DC voltage (much like a regular boost converter).
Vienna rectifier is boost-only. For a buck variant, check out a Swiss rectifier. You might also find these papers useful:

The Essence of Three-Phase PFC Rectifier Systems - Part I
The Essence of Three-Phase PFC Rectifier Systems - Part II