Wikipedia's policy stance against original research is intended to prevent editors from inserting their own opinions into articles. Our articles should be based on reliable sources without implying any conclusions derived from improper synthesis.
Invariably, articles will quite rightly draw from more than one source. So some forms of synthesis are allowed. It can be legitimate for a single compound statement to be supported by more than one source, even in cases where the complete statement is not a rephrasing of information found in a single individual source. Doing so can help editors avoid the appearance of plagiarism while also improving the quality of our articles.