It doesn't really seem that you totally understand the wastegate yet. You mostly have it opposite.

Yes, the wastegate allows exhaust gas to flow around the turbine, so you do not produce positive boost pressure.

The wastegate actuator has a diaphragm inside it, which is connected to the rod which opens the wastegate. The actuator receives boost signal from a vacuum line. On some cars, this vacuum line comes from the intake manifold area. On other cars, the vacuum line comes from a port on the compressor outlet.

When the actuator is receiving vacuum or less than 5 psi boost, the diaphragm acts as a spring which holds the wastegate SHUT.

When the actuator is receiving POSITIVE boost pressure of over ~5 psi, then it starts to OPEN the wastegate.

This means that most of the time, the wastegate is closed. When you are at full throttle, some of the exhuast gasses are bypassed around the turbine which then limits the amount of boost to about 7-8 psi in stock form.

Greg