This is the strap wrench that I have used several times to remove insulators that were stuck on a rusty or corroded threaded metal pin. I also used it at least once to remove a glass insulator from a wooden pin.

I've had good luck by dosing the insulator and metal pin with PB Blaster (essentially WD40 on steroids). Wait a few days for good penetration. Clamp the pin in a vise with jaws padded with soft pine blocks.

Get a strap wrench to apply torque to the insulator. Take it easy. Work it back and forth to break loose the interference fit between the pin and the insulator.

For a wooden pin, let it sit inside to get dry. Perhaps it will shrink as it dries out. Skip the PB Blaster for your first attempt.