Not certain on the size of a 6 metre, but it sounds similar dimensions to an A Class.
My A Class weighs 15Kg and is about 1.7 metres long, the boat is about 2.5 metres tall from keel to mast crane. I have a lifting eye on the deck directly above the keel at the balance point. I then have a (removable) hook handle that allows lifting and carrying the boat. I usually wade in a little to launch,
For your situation, I would be very doubtful about launching the boat when the water was that far below the jetty. Maybe a longer hook handle....?
I would not consider lifting the boat by the rigging - while it would likely hold, it is just asking for trouble, either stretching the rigging or tearing a chain plate out if you get a gust of wind at the wrong moment.