My understanding is that they only looked at cardiac patients, so that wouldn't contradict the study.

It might depend on how risky the surgery is in each discipline.

I'd expect heart and brain surgery to be among the riskiest, whereas other types of surgery might be significantly less risky. I wouldn't expect most cancer patients to die from their surgeries, for example.

Would depend on, among other things, how easy it is to "schedule" complicated cases. For some specialties this is straightforward, for others, it's not.

See mortality during the Canadian physicians' strike.