My Roubaix feels stiff. But I'm coming off riding a Miyata steel frame that flexed a lot when I was sprinting. So it's in the eyes of the beholder. If my friend owned a Trek store, I would probably be riding a Trek Domane. But I don't think it would ride as smooth as my Roubaix.
I have the future shock and the S-Works CG seat post, and running 28 tires. I ride mixed roads of blacktop and gravel. I think it climbs well and rides smooth. And I certainly don't feel the Future Shock when I'm riding in any way. But I did notice that after a 30-40 mile ride on our rough patched blactop, my hands are not sore from the beating any more.
My 2 cents worth.
Joe