You don't mention what temp/degree of doneness you cook them too, but I find too-rare duck breasts to be tougher than I like.
Start skin-side down (and while I don't have a Jaccard, I use a sharp knife or trussing needle to piece the skin in multiple places) in a cold pan, and let that sucker cook on low-medium heat for quite some time, in order to render plenty of fat out. Turn over when the skin is nice and crisp and complete cooking to medium-rare to medium, and see how that works.
Two duck breast dinners...
No problems with tenderness.
