Starship structure by era question

Structure as it stands in starship construction doesn't make a lot of sense. A 23rd century Constitution class and a 24th century Galaxy class have the same amount of structure despite nearly a century worth of technological advance in materials, structural integrity fields, et plus the fact that the Galaxy is something like eight times the mass.

What is the general opinion on how to deal with this flaw in the rules? Everything else is era-regulated by availability date.