Are my questions really so bad or is it possible that a particular user is extremely nitpicking on my questions, say, mithilfe+Genitiv OR mithilfe+von+Dativ? ?
The StackExchange question & answer model has a great advantage over other sites in that a post is not only judged by the community but that it is also many users who - with their votes - make clear which posts are great, which posts are mediocre, or which posts need an edit for improvement.
It also is the community who with their votes decide on the on topicness of questions asked here. To do so we had a lot of Meta posts to define what topics we accept and what not. Sometimes the line is not so clear-cut and sometimes there still is debate where to draw the line for off topicness. This lively discussion is a good thing.
Still, it is not a single user but the community to decide this.
So from your many posts so far there are both, well received questions with many upvotes, and questions where the community felt an edit was needed. Often you will be asked for this in comments. From these comments the level of politeness is very different amongst our user base as much as our users come from very different cultural backgrounds. Please also keep in mind that for most people here English is not their native language, and language skills are hugely different. Nevertheless, if you don't follow the advice given or explain otherwise why you prefer to leave your post unchanged there is very little hope that the community members involved will change their mind on the quality of your post.
In the end it is you who came here seeking for an answer to your question, and it is the community members who with their spare time voluntarily try to give you an answer to the best they can. This deserves all our respect, including our good will to follow the rules this community had defined regarding the scope they are willing to contribute.
So my advice to keep having fun in our community would be to try your best to help people help and to stay away from people that made you feel bad.
Oh, and yes, do continue to flag rude comments because only then we will be able to take the necessary action for people who show continued rude behaviour.