Giving players so much freedom that they can easily identify and execute a grindy, brute-force but boring strategy is an extremely common problem in game design. Fault is irrelevant, it is the game's problem if the player stops having fun because they got trapped in a psychological pit tying to circumvent the rules when playing by the rules is ultimately easier.
This is a tradeoff so requires some balance, but OP's suggestion is simple, unobtrusive, and probably effective.
Exactly. That's also the same reason why a game being too easy is the game's fault. One could object that players should be more disciplined and intentionally forego (e.g.) the stronger weapons in the game. But part of the fun of playing the game is to try to get the best possible weapon. Similarly, it is little fun to play e.g. tennis or chess against a weak opponent. Either it is too easy, or you don't give your best, neither of which is particularly fun.
The whole purpose of a game is to complete a goal. Good games gamify you to achieving that goal. If the goal is to learn CSS and the game hasn't guided you to achieve that goal then it's failing at its purpose. Blaming the player for not playing correctly is an unbelievably bad take. The mechanics of the game should punish the user for doing the 'wrong' thing and reward them for doing the 'right' thing.
Giving players so much freedom that they can easily identify and execute a grindy, brute-force but boring strategy is an extremely common problem in game design. Fault is irrelevant, it is the game's problem if the player stops having fun because they got trapped in a psychological pit tying to circumvent the rules when playing by the rules is ultimately easier.
This is a tradeoff so requires some balance, but OP's suggestion is simple, unobtrusive, and probably effective.