Advances in the last 50 years in materials, cabinet design, drivers, crossovers, and enclosure and port modeling. Those are all incremental. The few pre-1970 designs that are still competitive are all high-end, high sensitivity horns, like JBL, Altec, and Klipsch, and even thos have had significant refinement over time.
The JBL 4367 is a vast improvement over the L-200/L-300 in bass, smoothness and extension. The remarkable dynamics and ability to fill large rooms still remain.