If you want to really spend time in a place, cruises don’t cut it. A good example is a vacation we did to Normandy. We spent a week there seeing the sites, and enjoying the local cuisine. On the way from we stopped and spent a day at Versailles, going back to Paris, we visited Giverny to see Monet’s garden.
When I imagine a cruise to Normandy, it would be 8 hours to see whatever highlights that can be fit into that time period, which if you were going to see a beach landing site, visit a cemetery, and one of the significant towns say Sainte-Mère-Église, along or near the coast, this might be enough, but as you said, it would feel rushed, even though we enjoy cruises for certain experiences. A 2 week Med Cruise, covered more distance and we saw more sights than we could hope to do on our own in one vacation.