I don't think you understand the principle of how you get power. Burning fuel get you power, burn more fuel, get more power. To burn more fuel you need more air (the oxygen you need), so, in N/A engines, higher RPM means more air and that means more power. Max fuel flow is at max rpm, by definition.
For turbo engines it's the same, more fuel is more power and for that you need more air. Because you don't need to suck the air in with the pistons, but push it in with the turbo, rpm or even displacement is irrelevant. In turbo engines boost is the dominating factor. more boost is more air is more fuel is more power.
With N/A engines air intake was regulated with the displacement at first, making that all manufactures were searching for even higher rpm's, until they really caped this off with a rpm limit.
With turbo engines of any discplacement and/or rpm with unregulated boost, power is in theory unlimited (remember, boost=power)
so, in other series they choose to limit air intake by restrictors to prevent unlimited power and have weird engines but opted for a fuel limit. Also because rpm is in theory also unrelevent, they have set a value that still sounds like more or less a racing engine and that is that 10.500 rpm. A value that is easy to manage with current tech, without any trouble of blowing up engines or the need of next get technology.