"Anticipating potential astronaut transport needs, Falcon Heavy is also designed to meet NASA human rating standards. Falcon Heavy is designed to higher structural safety margins of 40% above flight loads, rather than the 25% level of other rockets, and triple redundant avionics. Despite being designed to higher structural margins than other rockets, the Falcon Heavy side booster stages have a mass ratio (full vs. empty) above 30, better than any launcher in history. By comparison, the Delta IV side boosters have a mass ratio of about 10."
There's no taking away from "better than any launcher in history". On the other hand, the comparison to the Delta IV isn't as informative as you might think it is. Falcon uses kerosene for fuel and kerosene is quite a bit denser than the liquid hydrogen used by the Delta IV. Liquid hydrogen not only needs a larger tank, that tank also needs to be heavily insulated. One consequence of this is that you simply can't get as high a mass ratio with liquid hydrogen as you can get with kerosene. On the flip side, hydrogen delivers a higher specific impulse, so extra tank weight is offset by fuel that is substantially lighter.
It's all the more impressive when you realize that the Falcon series to designed to (eventually) be reusable. Now, the mass fraction won't be anything like as good as the expendable version, and the turnaround time will be significant, (you'll have to sea-recover each stage, install new seals, and reapply the heat shield; but the STS also has a turnaround time for the same orbiter measured in months, even with their reusable heat shield and dry-land capability) but they've given themselves quite a lot of margin.
