Stand corrected, but if modern blades thinner and have more flex, how does that affect how they work in vintage and modern razors? The EJ 89 was supposedly copied off a vintage razor, as is the AS-D2. Maybe the designs of the Timeless and Rockwell, perhaps from the ground up, take account of thinner more flexible, modern blades?
That would depend on the head design and geometry of the razors in question. If a razor fully supports the blade it will hold the blade in a rigid state no matter the thickness. If a razor lacks support, a thicker blade will be inherently more rigid.
The first two pictures are of vintage Gillette NEW razors. The NEW SC on the left and the NEW LC on the right.
Notice the profile of the base plates. The SC fully supports the blade on the base plate with the cap locking it down very close to the edge of the blade like in a vise. The LC on the right, has its pinch point considerably further back and for me shaving ATG over my trouble areas, allowed the blade to flex and skip off the stubble instead of cutting it cleanly as the more rigid SC does. If modern blades were still .006" thick or thicker, that would be less of an issue with the LC and not sure it would affect the SC at all.
The Rockwell razor I dont see as a rigid design, but I understand many people get great shaves from them. I'm not sure Timeless designed their razors around the fact that blades have become thinner, but I think they believe that a rigid blade edge will give a smoother shave as its inherent to their design. I dont think I've ever read from any of the many Timeless razor owners on this forum complaining of a lack of smoothness.
I believe that a more rigid design will help many people with shaving ATG. I certainly does me. I gave my NEW LC away, but my SC is my favorite razor.