I hesitate to say anything is cheating. If it is the honest efficient way to explore an idea, than you should do it. That said, I don’t think CAD is truly the most efficient way to explore any idea for the following reasons:
- it encourages depth exploration vs breadth, potentially locking you into a solution and trying to fix it vs finding the best solution
- it is a solitary activity compared to sketching which can be done in groups and easily shared, talked about, and feedback/workshoped
- your form language tends to be highly dependent on your platform/skill level. Might be fine while minimalism is in, but it will change.