A RC servo is very different from an industrial servomotor. The former is a compact module consisting of motor, gearbox, position sensor, and electronics usually with a Futaba compatible 1ms - 2ms pulse control signal, whereas the latter consists of a low inertia motor, tacho generator, and usually an encoder all on the same shaft, with a completely separate servo controller.
The PCA9695 output levels are determined by its supply voltage, and as 3.3V pulses may not work with all RC servos, it would be preferable to run it with 5V supply and level shift the two I2C input signals rather than having to level shift 16 output channels.