I would like to add that decisions on which candidates in what field are being accepted can have many, many reasons. One being, hypothetically speaking, that the professors in one field have been taking on many students in recent years, and others not so many, and that it might be their turn to supervise somebody.
This doesn't necessary reflect any broader policy or judgment on the state of Art History. That can be usually gauged by things such as who is teaching, who is being hired, etc. The best programs will have to, and generally do, aim for balance. And that's how it should be.