I’m sure this is simply history repeating: being fluent, being accurate.
What does it take to conjoin the two qualities in oral and in written expression? Well, it takes discipline and compliance. It takes a lot of acceptance of linguistic resources AS THEY ARE: no inventions, no attempts at distorting what comes in ready-made constructions; in one sentence: don’t ask why; just take it as it is (well, that was two sentences!).
In the attached pdf you’ll find the abbreviations I use when correcting. It saves quite a few hours of correction per campaign. So you are asked to download it: it will be helpful when time comes for you to decode your marked writing tasks.