last one I have that was really stuck I used a screw clamp in spread apart mode, but a piece of wood and a prybar usually works.
the main problem is the plugs/sockets float in their mountings, so rocking sideways doesn't transfer to the pins as much as you'd like.
if ya pull a pin out of the housing, or worse, crack a housing, not much you can do about it. The thing needs to come apart, even if it means having to source a replacement plug/socket. If ya just damage one pin, you can move the wires to a good unused one (if there is one), or you can swap the pins if you fiddle around figuring out how to release them from the housing.