No. The constraint is due to the limited processing power of the CPU, it is not possible to change that.
You seem to be misunderstanding how Myxa works, which is important to rectify before you proceed with further testing. According to the screenshot, you are using the voltage control mode. As explained in the quick start guide, the PID controller is only used in the RPM control mode. Since that is not used in your case, the PID settings will have no effect on the operation of the ESC. You can picture the inner control loops per operating mode as follows:
In the RPM mode: RPM setpoint → RPM PID controller → current setpoint → current controller → voltage setpoint → motor
In the current control mode (not suitable for fixed-pitch multirotor vehicles): current setpoint → current controller → voltage setpoint → motor
In the voltage control mode: voltage setpoint → motor
If you are using Myxa with a multirotor vehicle, the voltage control mode might be the best choice excepting certain special scenarios. In this mode, the only parameter governing the bandwidth of the controller is the voltage setpoint slope limit, which is set via the parameter m.voltage_ramp. You seem to have left it at its default value, which is rather conservative. Consider increasing it up to about 25 volt/second.
This observed relation between the bandwidth and the number of poles is incidental and should be ignored.