Most passenger cars don’t really have bucket seats. Bucket seats like in race cars have hard, deep structural sides, whereas in passenger cars they’re just soft pillows in a very shallow bucket shape. This is obviously because getting in and out of an actual bucket seat is difficult and consumers don’t like it. Because the pillows are soft, they’re not going to stop you from sliding out in an impact.

I imagine the vaguely bucket shape of modern passenger cars has basically nothing to do with safety, at least not in the “stops you from flying sideways out of your seat” sense, and is mostly just a comfort thing.

I mean, isn’t that what the seat belt is for? I can’t imagine the typical front seat in a modern car keeping you put in a collision either. They’re definitely shaped comfort-first, and at best keep you from jostling around on uneven roads.