Firstly, I applaud your efforts, and I ask that you continue!
Now, I took APCS in 2012 as a senior in high school. It allowed me to place out of the introductory CS course at the University of Virginia, and it placed me onto a path of being a CS major.
We used a website known as eimacs[1]. This was quite similar to what you are doing (I believe). The textbook would introduce a concept, and then it would ask us to play with it in a built-in compiler. Immediate feedback was great!
Additionally, there would be a variety of the dry puzzles which you describe. Luckily, my APCS teacher realized the dullness of these tasks, and he assigned labs which were more fun.
I agree with the user "teach." Your process creates students who are 1) interested in coding and 2) can solve puzzles with code. It does not create students who are ready to take the AP CS exam. The difference is akin to students who do well in high school math courses but have difficulty with the SAT.