For each type of cancer, there are morbidity statistics. One thing is for certain. If you don't have a good Oncologist working on your case, the greater the chance you will die, but not everyone who goes untreated will die from the cancer. People have been known to go into spontaneous remission although it is rare. If you have the best Oncologist in the world, your chances of survival would increase, but even the best Oncologist loses patients (and even some that they are sure they can save). The morbidity statistics are the big sample size and give you the best indication of chances of surviving. No one would Google the survival stats and see a morbidity likelihood of 65% and conclude that the quality of the doctor doesn't matter.
The outcome of a game is much less certain than the outcome of a cancer case, but you give yourself the best chance of winning if you have a good manager who consistently makes the high percentage and smart moves. The additional games that the good manager will win for you as opposed to a dumb ass manager is very difficult measure with accuracy.