There is nothing, especially a VFD, that can make a 3HP pump produce more than 3HP worth of water. There is at least 5% inherent losses in a VFD, which increases slip in the motor, which decreases the max amount a pump can produce. In most cases, the VFD will produce less water from the same pump as a CSV. It just can't get to max speed because of the increased slip. Also, because of these inherent losses the minimum flow needed to cool a pump controlled by a VFD is much higher than when using a CSV. So the pump would actually cycle more for house uses less than about 5 GPM with a VFD, as that is how much it takes to keep the motor cool.
One advantage of the CSV is that you can bypass it. For zones that are large enough to keep the pump from cycling, just tee off before the CSV. However, on smaller zones like number 3 and 4 the pump will cycle on/off, as those zones are not using the max flow the pump can produce. And even though the CSV is not preventing the pump from cycling when using less than 3 GPM, it is still cycling much slower with the CSV filling the tank at 3 GPM than without a CSV where the pump would fill the tank at 40 GPM.
If you can make all your zones large enough to keep the pump from cycling off, then you can tee off to all the irrigation after the CSV. Then the pressure to the heads is only limited by the amount the pump can produce while working with no losses from any type of control. If you drill out your "water saver" washers on the showerheads from 2.5 to 3 GPM, the showers will see could strong constant pressure from the CSV as well. I find with the so called "water saver" washer drilled out people can get the soap washed off quicker and actually do not use any more water during showers. They just take quicker showers.
In your case the CSV is not so much for delivering constant pressure to all the zones, but more to keep the pump from cycling itself to death on the smaller zones, as all the zones are not matched to the pump.