Yes, I think some seats probably do a better job of protecting a child in a crash than others. The problem is, I have no idea which ones they are. And until I win the lottery and buy my own test sled, I'm not going to know. And even if I could run unlimited crash tests and determine which seat I thought was safest, the safest seat could change depending on the circumstances of the crash.
The fact is, we don't KNOW whether any seat is safer than any other. Some have features which certainly seem like they would enchance safety, like EPS foam or wings that cradle the head. Some have stiffer shells than others. But we don't really know what that means in terms of protection in real world crashes. Who knows - maybe that "flimsy" shell could turn out to be an advantage in some crashes because of its lighter weight and flexibility. Or maybe there's no difference at all.
My point is, we can't answer your question. That is why you always hear the answer "The safest seat is one that fits your child, fits your car, fits your budget, and that you will use corerctly every time." We can tell you which seats we like better. We can tell you which seats have features that may improve safety. We can tell you which seats best meet your particular needs. But no one can tell you with any certainty which seat is the safest.