Speed differential is not the whole story.

What is also important is the nature of the collision. A glancing (side-swipe) collision, is very different from a direct collision. Also in right-hooks, the most common collision of all, you have a cyclist colliding with a slowly turning car while typically braking and turning at the same time.

But even if we're talking about direct collisions, the cyclist often ends up going over the hood or roof of the car simply because of the height of the bike vs the car. This looks awful but is actually better than hard impact.

There are more factors than mass and speed differences.