As a number of commentators correctly suggested, the appropriate quality for the documentation depends on its intended use. Certainly information sent outside the organization should be as close to perfect as possible and "two sets of eyes are better than one."
This wasn't the core issue, though. Sebastian is proofreading and correcting minutes, notes and other internal, short-lived documents to the same high standard.
The purpose of technical documentation within a project is to get ideas across in a way the concerned audience can understand. Sebastian's team may need training and support to create effective documentation, but striving toward perfection doesn't add value.
The key to solving this problem is helping Sebastian understand that continually criticizing people for not achieving perfection can be extremely debilitating and will reduce his team's effectiveness. This is not his intention, but is the perception of people who receive Sebastian's heavily corrected documents.
The ideal solution is to get Sebastian to understand how detrimental his behavior is. Achieving this may require people who Sebastian sees as experts and advisers to coach him to improve his team-management skills.
Alternatively, effectively "advising upwards" by focusing on Sebastian's real interests, such as product delivery, may be a solution. Neither of these options, however, is likely to provide a quick solution. Changing habitual behaviors can take years and requires the person making the change to want to change.
A more practical alternative may be to reframe the problem. Written communication is only one way of conveying information. Alternative approaches may include scheduling brief discussions to resolve issues, using web portals to make documents shared resources where everyone contributes or changing the media to something where grammatical structures are less important.
Unfortunately there are no easy answers to this problem. For those on the receiving end of Sebastian's corrections, recognize that a criticism of a document you have written is not a criticism of you and use the opportunity to improve. (You should see what the editors do to our posts...LOL)