For the most part, Classic was designed by committee with many concessions to every corporate partner, retaining compatibility with their IrDA stacks, etc...
...while LE was designed by a few smart guys working together
This is about the newer LE 2M PHY, which was added for "replacing Classic" (which is 2-3M) use cases. It's not surprising that it's not as efficient as the more widely used 1M PHY.