I think anybody attentive enough to read that box will have read the rules already. If we want to eradicate posts missing descriptions, we need to be forceful. Personally, I would be happy with:
1. Enforcing a minimum post length for RMT of 1000 characters. Exporting a team of six from Showdown will give you about 800 to 900 characters, so this would be effective. Characters accrue quickly when you start writing actual sentences to where I think there are effectively no drawbacks with this idea, even for formats that require less than six Pokemon.
2. Scare tactics. Put a red box on the submission page warning that we remove ~70% of submissions to RMT for not following requirements (yes that's an accurate figure), and the only way to ensure you get it right is to spend one minute reading.