May have been just an isolated experience, but I self-studied for the Physics 1 exam after a year of regular-level physics and got a 5. I am very good in physics though (I got my highest grades so far in my two semesters of physics).
Could just be that the depth of material covered was a huge difference from Phys B. Phys 1/2 had less material covered than B, so the CB probably made it harder in terms of solving the actual problems.
Basically, the new courses seem ideal for students who excel in algebra and physics. And besides, other science courses have high-ish rates of failures anyway. Bio has a 35% fail rate, Chem a 48%, and Env. Sci a 55%. These courses are just very in-depth, I suppose.