Seven has a huge repository of knowledge, but frankly, I've always thought as her as the defacto chief science officer, which, surprisingly, being a Science ship and the Intrepid Class being the replacement for the Oberth Class, not have a prominent chief science officer always seemed weird to me.
For a show which allegedly focuses on exploration, Star Trek always had a weird way of portraying science officers. The original series and Enterprise had the science officer be the first officer as well, as if science wasn't interesting enough on its own. In The Next Generation, science was more or less the Ops Officer's hobby. Deep Space 9 had a science officer which didn't do much science-ing and Voyager had none.