Airbag deployment is an extremely violent event. YouTube is replete with videos featuring people who attempt all manner of stunts with them. Here’s one. If it can launch a man like that, it’ll certainly punch your legs back toward your face in a big hurry. In the best case, your knees would clear your face and just come back to your shoulders. More likely is that your knees will hit your face, or that the load from the deploying airbag will be unevenly applied to your legs and break your tib/fibs, and/or will cause your legs to fly away from the dashboard at angles that result in severe knee/hip injuries.
Even in the absence of an airbag, a crash would be bad news. The seat belt keeps your head and torso from striking the dashboard, but they will at least partially close the gap. You may strike your head on your knees, or your feet may slip off the dashboard high, and strike the windshield, or your feet, or they may slip off low and you’ll strike your shins on the dashboard, breaking tib/fibs.
And then of course there’s the matter of the lap belt riding high because your pelvis has to tilt to allow your thighs up.
All in all, yes, it’s likely to create substantially more severe injuries in a crash, with or without an airbag.
Edit: here’s an even more energetic airbag deployment.