Below is what the tour description says. Indeed... there are quite a few drive-by's... but it says some time at the 9/11 Memorial.
If one could 'exit' the excursion after say the Memorial visit... to remain in the downtown area.. might be worthwhile to get the 'lay of the land' via the tour itself.... and at least at chance to do something in the Manhattan area (i.e. a lunch or meal) before leaving for a later 7:30pm-ish flight. i.e. attempting a "Day Trip".
My 'shot in the dark' with this post is if maybe someone else has taken this tour (or similar) and can briefly share their experience. Perhaps, this ship sponsored excursion gives an earlier/guaranteed departure (i.e. 9am or so)... that could save some time competing for a taxi/Uber/ferry at the cruise port itself. Otherwise, it is difficult to book with Viator (or similar) on disembark day as those don't seem to meet anywhere near the Brooklyn port. It's difficult to determine the time and when to book with one of the external travel companies. Plus... need to work out some way with a hotel (??? or somewhere ???) to temporarily store luggage for a few hours.