I've seen a few different scenarios on good psi but not enough volume.
1) Using a dyno with 1 fuel flow meter. Motor would not rpm and ran like poop over certain rpm. Fuel psi gauge on dyno console and fuel psi gauge on fuel line just before carb fittings both showed 7psi.
After much investigation, phone calls, different dyno fuel system parts we made full dyno runs while I stood next to the motor with an eye right in frt of the fuel bowl glass window - thanks BG for clear sight glasses ! The fuel level would drop, come back up, and then turn into a frothy mess !
Removing one part at a time on the dyno fuel system, when we bypassed the fuel flow meter the frothy mess disappeared and the engine came right back to life without missing a beat.
So, the fuel psi gauges where showing correct psi, unfortunately air psi was part of this.
2) Cracks or poor sealing with fuel tank pick up tube and/or pump inlet line. PSI shows normal, but again there is air in the system.
3) Needle and seats not flowing enough fuel. PSI shows normal, but float bowls are emptying.
It is my belief if there is a restriction or issue before the pump, the fuel psi gauge may not be influenced. However, if there is a restriction after the pump, then the gauge typically will be influenced. Although, that dyno experience had the fuel flow meter after the pump so I still won't 100% believe if a fuel psi gauge shows correct psi that it is actually all fuel.
Got to love those large and clear fuel bowl sight glasses ! Really saved our azz being able to see what's happening in real time in the carb - where it counts.