If you cut all the way down to the cockpit sole, then you also have the world's best drain. I have sailed sailboats with this "open transom" design and yes, they do take water in in bad conditions, but it leaves again in a hurry. And of course, under sail you are deliberately doing stuff that risks water coming aboard....
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida