With the engine at wot, at whatever rpm that is.............. the output and the load are in a state of stasis.
They are equal. In order for the rpm to change........ something else has to change to allow that to happen.
Either the output or the load.
Since the load curve climbs rather steeply with rpm, in order to raise the rpm from the point of stasis you’ll need to make enough additional power to exceed the rate of change of the load curve.

To lower the rpm, close the throttle some, rpm will drop.

If you closed the throttle say, 1/2 way....... the rpm would drop to the point of the equilibrium between the new 1/2 throttle output and the equivalent pump load.

It’s much the same as the beginning of a dyno pull with a water brake.
Let’s say you want to start the pull at 3000rpm.
You start applying throttle and load together until you get to where you’re at wot, and the engine is steady state at 3000(or just under).
In order for the engine to actually accelerate and make the pull, something has to change, or the engine will just stay at that rpm.
Since you’re already at wot...... you can’t just “make more power”....... so you have to start releasing the load to allow the engine to run at a higher rpm.

With the jet pump, there is no releasing the load........ so if you want the engine/pump to turn faster...... you have to make more power.

To take the analogy a bit further....... once you had the load valve on the dyno set to apply the necessary load to hold the motor at 3000rpm........ you could back the throttle off and the rpm will fall off.
You could keep going to wot over and over again....... but wouldn’t get past 3000rpm because that’s where the power and load are equalized.
So, let’s say that you did that initial load valve setting with the timing 10 degrees less than what’s optimal......... and then you put the correct timing in the motor. Now, that motor makes more power at wot it will go beyond 3000rpm because the output has exceeded the load thats present at 3000rpm.