When considering steel the amount of material also comes into play as well as the actual material composition.
A heavier bike most likely will use a cheaper lower tensile strength steel (not to worry, still plenty durable for bicycle application). This means the wall thickness needs to be greater. This can then lead to lessened "suspension" in the tubes as they are thicker hence creating a harsher ride than a premium steel frame would. With better steel thinner tube walls can be used making a more compliant and road buzz damping frame.
I'm pointing out here that rarely is weight the only issue at work in premium bicycles. Of course a lighter bike will cost more, but you also get other things than just the weight. With carbon you get aero benefits and all that. As mentioned earlier higher end models usually sport higher end components which to a certain point are more durable, function better and especially with wheels give again, some aero benefit.
Weight is just one part in the sum of incremental performance improvements. One just needs to decide what performance index is sufficient. I'm not going for over 9 kilo road racing bikes again. It's pretty easy actually to get under 9kg with a road bike. And my lower limit is at the 6.8kg which is the UCI mandate (not going there any time soon). With a touring bike things are of course different if they are going to incorporate disc brakes and rohloff hubs.