Hmm. Interesting. The second example is from a video that also includes the code to run the system, but he didn't mention anything about issues with loop timing. What sort of problems do you foresee? Here's the video link in case it's helpful: How to Build a Simple DC Electronic Load with Arduino Part 2 - YouTube
From what I read about the Zero board, the A0 pin supports true analog output when using analogWrite(). This is what was used in the video as well, but am I mistaken in interpreting how this functions? Would you also be able to elaborate upon what you mean by the board missing a voltage reference for the battery?
Thank you for your reply and other comments/suggestions too!