I understand what you saying and concur actually as someone stated before pressure builds after resistance. Actually what your looking at per viscosity and flow rates is max resistance it can take before the motor goes in to stall. Once in stall it overheats and stops working.
So taking a high flow rate unit and restricting it down and maintaining that just isn't the best way to do it.
Then you get into marketing and how things are rated so they can be sold. Holley Sniper as an example doesn't state flow rates, yet that is what the injectors need. Certain flow at a certain speed to develop enough pressure to spray into the throttle body while the engine is running. Or no vroom vroom. So what does Holley specify?? 58 PSI. If that is the case then there has to be a pump that specifies ... 58 PSI, or some verbiage that leads you to believe it would suffice, otherwise..., why would you buy it?
So I concur with what you are saying, but if OEM says it is a 9 PSI pump, and the pressure return is set from the OEM at 9 PSI, and someone asks what pump should I get??? I wouldn't suggest something rated at 39 for something only requiring 7.5.
At atmospheric 14.7 psi at sea level get a 5 gallon bucket dumped on you or get sprayed with a 3/4 inch garden hose at 120 psi... Which one gets you wetter, faster? Each have their own specific flow rates and flow characteristics.
Simple terms if your carb needs 7.5 psi from a 3/8 inch diameter supply, get a pump (9 psi) and regulator (set at 7.5) that will work for that, then go drive it and see if that works.
You might find the 9 psi pump goes flat after a certain RPM. Then try the 15 psi pump, maybe flat spot goes away. This is why I suggested the 15 psi unit. The carb is designed for a mechanical system. So an electric at 9 or 12 or 15 can't handle that???