Surely you understand that there are price points to be met. The AMD APUs by themselves are a solid choice for a lower-end laptop that will actually perform well on some esports games. Adding a dedicated graphics chip pushes the price up significantly, and the customers buying that level of device are more than likely not looking for an APU to be handling the computing portion of the workloads.
There really is no sense in in mixing an APU with a dedicated GPU unless it was part of an upgrade path in a desktop computer. (you were specifically mentioning laptops)
This is completly true. Especially with MXM, as MXM cards are absurdly expensive. As far as APU based laptops... They are supposed to be cost effective and budget oriented. If you get an APU machine for $400 and compare it to an Intel machine at the same price the APU will decimate it in 3D acceleration. APUs aren't meant to be ultra high performance. They are a way to get a laptop that is inexpensive and can hold its own in medium - low to medium settings in esports games. AAA titles may run okay but you'll be seeing low settings.
This crossfire you're talking about ive never seen in a laptop. Crossfire between an APU and an add in board is possible... But you'd be seeing a very slight difference if any in supported titles. The fact that the add in card has to be on the extreme low end almost makes it kind of a bad deal IMHO.
The next generation of APUs are in the way, let's see what's in store for us.