Admittedly, I don't know much about modern speedboats, but the full flip probably saved their lives. In the old days, flipping onto your head at damn near 200 mph was certain death.
Yea that flip and rotation definitely saved them, you can see in the video they slow down drastically in the air while the top of the boat was pointing mostly forward, although they likely also experienced some drastic gforce changes as it happened.
The pilots suffered multiple fractures, including a broken knee.
I'd call a broken knee alone a serious injury...
Had their injuries been more serious, they may have been unable to escape the sinking boat.
Had the boat landed in a different orientation, or done a different, completely undpredictable, uncontrolled aerial manuever, such that it impacted the water with more speed, the boat could have broken apart on landing or become structurally comprised much more seriously, and thus the pilots would be sinking much more rapidly, likely with more serious injuries.
Though this boat and its safety cage performed admirably in terms of structural stability... similar crashes to this have maimed and killed a good number of folks in the history of hydroplane/powerboat events.