Yes we should update the course with Principled Shader info. But as far as is mixing components worth learning, *yes* they absolutely are worth learning. In fact I strongly recommend you do.
If you ask me it would be similar to someone who doesn't learn anything about the way their car works simply because it turns on and runs fine most of the time. But when it doesn't run fine, they're without a paddle if they don't know anything about what's happening under the hood.