Sorry if I repeat something discussed before.

I think you miss some of the advantages of the Pierburg valve. Lancia was just the first car to use the concept, now all new turbo cars does. As a turbo's waste gate has the turbo pressure working against a spring there are always an amount of leakage through the waste gate, even from very low rpm. Now the waste gate is kept closed by the spring pressure, the boost from the manifold will work against the spring and open the waste gate at the adjusted boost. The Pierburg is a 3 way solenoid one of the first 2 legs can be open to the 3rd. Pressure tapped from the turbo outlet goes through the open channel of the Pierburg and help the spring of the wastegate to keep it closed. Now there are no leakage and have a little boost pressure, way lower than before. When the planned boost is reached the ECU switch the Pierburg's solenoid, the channels change and now the boost from the manifold work against the spring to open the waste gate, keeping the boost pressure at the planned level. This gives a much more linear power supply without the huge shove in the back at 3500 rpm and it is much more usable on a track. The waste gate actuator used with the Pierburg, then will have a tube on either side of the actuator's diaphragm. I am not the electronic expert but the ECU do not just open and close the Pierburg but rather pulse it to open or close the channels a little. This stops the solenoid from chattering, due to open an closing on the boost limit.

An external waste gate have a larger diaphragm and the spring is then stronger to counter the larger force the pressure now supply. The larger spring allow less leakage and the control of a boost controller will be more accurate.

The only possible advantage to go without the Pierburg is to have less power below 3000 rpm, saving fuel in town.

The bleed valve is the crudest form of boost control and are only work satisfactory in some cases where the waste gate is set to a lower everyday setting and by opening the bleed valve the pressure will go to a higher boost pressure before the waste gate are opened.