French DDs are about knowing you have a great Saturation mechanic on your hull that makes you surprisingly tough to kill at lower health amounts. So you can use this to brute force a fight against DDs and win.
As for open-water gunboating, you'll want the +20% range talent for your Commander. You'll be able to fire comfortably at a good distance, and you can avoid shells that are fired at you by Battleships or floaty shell Cruisers.
I have a video that describes the technique:
Direct Video Link: https://www.youtube.com/watch?v=wwWOxYn59JA