Let's stop with the comparison to humans, I'm more interested in why it would hurt to train LLMs with harder puzzles. Isn't that what we're doing all the time when training llms? I'm just suggesting an easy way to construct new puzzles: just randomize the varnames.

An even easier way to construct new puzzles is to fully randomize the problem statements and intended solutions.

When you take out the information from the variable names, you're making the training data farther from real-world data. Practicing walking on your hands, while harder than walking on your feet, won't make you better at hiking. In fact, if you spend your limited training resources on it, the opportunity cost might make you worse.