I don't doubt that's true for sailboats that go to sea, or that race, where in the latter the skipper might be pushing the edge of the performance envelope, so to speak, but in general? I think open transoms are so popular b/c they make boarding & disembarking easier, especially with the boat tied stern to the dock. Serious cruising boats of older designs had all but no "cockpits"; areas very good at shedding water quickly but not comfortable for socializing. If you're going to buy a "social boat" you want a BIG cockpit. But for it to drain quickly enough for safety you have to open the transom. So, people like the open transom for its ancillary benefit of convenience, not b/c most ever anticipate sitting under a half ton of water hoping it will drain away before the next comber crashes on them from above, IMHO! The Bavaria, for example, has a fairly small cockpit in terms of volume; not comfortable with more than 4 people.