In theory, I agree with OP.
In a year like this one, though, it works great because parents and older children who work in non-Jewish environments have time off anyway, and can spend quality time with the whole family. (when the dates don’t coincide this would not work, because how would it sound to give the kids xmas vacation?!)
To Joseph and Squeak, you have obviously never been children or teachers. The school year, especially the winter, are a VERY long stretch and people really need a break. If yeshivas had shorter days and/or more recreational activities, vacation might not be necessary.