You're opening a whole can of worms here. Almost all commercial perfumes are a mixture of what nature has to offer and what chemistry has to offer. There are those people rabid, and I mean rabid, about using only natural ingredients (visit the board Natural Pefumes, eg), but they lack any kind of decent musk or ambergris for example as these are hardly available naturally or are outrageously expensive or unethical to use in the cases of musk and civet. There are wonderful things that chemistry alone has brought us for perfumery that are extremely long lasting that don't exist in nature. Take for instance the many wood notes.. well, mid notes and tops, too. The modern perfumer makes use of all of the things available. Synthetics certainly have the longevity of naturals ... and often better. You really need both. There is no problem combining the two.
Mike, perfumer in Los Angeles.