A shortcut to start Writer should call LibreOffice executable using the --writer
command line parameter.
Of course, using a template, as @Wanderer suggests, is also a nice (maybe a better) solution.
However, both would only be useful in case user only uses one type of Writer documents. Start Center allows one to easily access multiple templates, so whenever one regularly creates many different types of documents (mails, essays, whatever) - there would be no upsides in starting straight into Writer with some default document.