Okay, but is not cancer, it is tumor.
Anyways if the numbers presented are correct, it does form enough substantial risk for cats. Though doses and such are unknown. Risk is quite high vaccination wise, but not yet game of rulette as you described. Especially as the diseases vaccinated against form a risk too. You have just some absurd assumption that vaccination is the only risk for pets.
"The incidence of VAS is between 1 in 1,000 to 1 in 10,000 vaccinated cats and has been found to be dose-dependent."
https://en.wikipedia.org/wiki/Vaccin...ciated_sarcoma