Need help with theremin oscillator
For lower distortion, you need the PI network to provide some filtering. 

I think that requires the PI network be an effective low-pass network.

I think that requires the amplifier Rout be much higher than the PI capacitive reactance.

At 7MHz, the 1.2nanoFarad is

(1uF at 1MHz is -j0.16 ohms; 1nanoFarad is 160 ohms; at 7MHz, Xc is j20 ohms)

I agree with Andy ----make the resistor values at least 10X higher.