I believe this is a myth! You still very much have to care - for security updates.

However, more often than not, you've just lost visibility into what libraries and versions you're actually running..

Yep. The production box no longer needs to have the exact same library packages installed as the dev box, but now it needs the same docker images installed. It's just moving the goal posts - with respect to "dependency problems".

The actual benefit to containers is abstracted and unified software components in a complex system. But as we create new, different cloud computing tech, this becomes more difficult, and defeats the purpose somewhat.

Sure, but that should be part of updates. Even if developer doesn't take care of it, you can rebuild the image to update libraries. Of course app might stop working, but at least other apps/containers still work and you can revert the change easily.