I think both the idea and execution are great. These games would be useful even just as problem statements. I like that each problem clearly defines the desired tone and goals, and that the sample solutions have explanations.

Both in technical and creative writing, I agree that the main issue I've seen is unnecessary filler words, needlessly complicated sentences, and a difficulty clearly expressing the point and staying on-topic.

Some ideas - A copy of the original text with highlighted words above the editor might be nice - Not sure if the timer is helpful, might cause people to do a poor job for fear of running out of time. Could start without a timer and add it in as users get more practice