Yes, but in those 60 years subsonic performance also improved by a gigantic margin. And yes, there are real physics problems that make it hard for a plane to be

Yes, but in those 60 years subsonic performance also improved by a gigantic margin. And yes, there are real physics problems that make it hard for a plane to be excellent at everything, a wing can't be optimized for everything, and neither can an engine. And if you are using the methods used in this experimental plane. You gone have to drop out even more seats making the per seat efficiency even worse. The Boom Supersonic plane is a new design and even their outright fantasy future projections (that are unlikely ever to be true) don't make the plain as efficient as subsonic travel.