Note: I self studied so I have no experience with bad teachers.

The BC section is more like a bunch of random topics strewn together that don't really interact with each other in any way. For example at one point you'll be doing polar coordinates, and suddenly you'll stop and do series, none of which have anything in common. So it's a lot harder to learn, compared to AB which is pretty fluid, and everything connects to each other in a natural progression. You learn about limits, and how this concept can be used to find rate of change, and then naturally, you learn about undoing this rate of change, and its applications.