The Concorde is not "average", it is the most fuel efficient supersonic aircraft to date by a huge margin. Yes it's kind of old but I think you are dramatically overestimating how much aircraft turbojet engines have improved in the past 40 years.

While Concorde was efficient at supersonic cruise, it was ridiculously inefficient getting there (and this was one of the main arguments for the proposed Concorde B).

Also note most aircraft capable of supersonic cruise nowadays don't use turbojets, they use low-bypass turbofans (mostly around 0.3:1).

turbojet is not the only thing that can be improved to reach the overall 10x.