Even MAP systems will go open loop under full throttle.
Aside from you saying so, why would the turbos not have the over spool risk. You stated they spin up quick because they are small. You have a sudden volume or pressure drop on one side (compressor) of a turbo and a constant pressure on the other side (turbine), the turbo will spin faster.
A turbo size is not the only factor in spool up time. turbine and compressor pressure, air volume, flow pulse.. a lot goes into it.
The bottom line is the ONLY advantage is you get an early 2000's type BOV sound. Being that the possible risks are not factually dismissed but more of an opinion or educated guess.. why risk it at all?
This is the same crowd doing annual complete fluids flushes but is onboard with this mod. I'm so confused.