Your point is valid but you can also prove you can accomplish something while also actually accomplishing something meaningful. For example you complete one of your side projects instead of a meaningless assignment. Sure, the side project might not actually succeed, but at least it had a chance. I also feel like 95% of the key to learning are hard deadlines with consequences.

Also, to varying degrees, every justification for doing a CS degree has smelled like an attempt at rationalizing a poor decision.