Getting off the ground is tricky from the undercling. The real tricky part is the mantle though. If you choose to do it from a heel or standing on the hold a bit lower is up to you! It is all in turning the hands at the right time!
Rain sucks, but broken holds suck even more. Remember, never climb on wet rock in Fontainebleau.
The sandstone becomes brittle, and pulling on it will ruin classic problems. Drying it doesn't help, because it's still wet and weak inside.
All you can do is wait for better conditions.