According to IOM, PRISMA, and Cochrane standards, to write a truly comprehensive systematic review, librarians should be involved in designing the search, executing the search, compiling the citations, creating a search strategy appendix, and writing the appropriate portion of the methods section.
If the systematic review methodology is not appropriate for your question or the breadth and depth of the research you intend to undertake, there are other review types that may be better suited for your purposes.
There are many instances where your research topic may not be best suited to performing a systematic review. You may not have the time, money, or team resources to perform one. Perhaps your question has not been well studied and you do not have a critical mass of studies to pool in a systematic review. There are other, just as valid, review methodologies you can write instead.