The thing to note about OTAs is that they output current - not voltage. Resistor RL in the schematic is there to convert the output current to a voltage for driving the darlington pair buffer.
Here’s my take on an lm13700 based VCA that accepts control voltages up to about 10V:
U1A and U1C do the current to voltage in this design, I don’t use the lm13700 buffers.
The bias current (I_ABC) that does the volume control is provided by the op-amps driving the pnp resistors which act as voltage controlled current sources.
Cheers,
Jared