I agree with what you said,
the way I look at it, while the stock turbo will continue to produce more power past 12 psi, the efficiency of the power increase however, will decrease as you raise the boost past 11-12psi
ie; the extra power gains to be had by pushing past 12psi are not worth the risk of added strain on the stock turbo.
All cars are different though, some guys on here will boast about having 14psi+ on stock snails and still going strong, if a turbo is gonna die it will die eventually, but adding extra fuel to the fire isn't going to help the situation imo
hi flow or bolt on replacement ftw if you want to chase the dragons