How prevalent are abusive advisors?
From PhDs: the tortuous truth:

Overall, 21% of respondents said they had personally experienced
harassment or discrimination, and the same proportion reported
experiencing bullying. One-quarter of respondents who identified as
female reported personally experiencing harassment or discrimination
compared with 16% of those identifying as men. The highest rates of
harassment or discrimination (24%) were reported in North America, and
the lowest (18%) came from Australasia.
...
In the survey, 57% of students who said they had experienced bullying reported feeling unable to discuss their situation without fear of personal repercussions.

From A message for mentors from dissatisfied graduate students:

In the survey, 21% of respondents reported experiencing discrimination or harassment. The same percentage also reported bullying. Of those, nearly half said that their supervisor was the perpetrator

It looks like, by the numbers, 1 in 10 PhD students will be harassed or abused in some way by their supervisor. Anecdotally I think that abusive advisors burn through students at a higher rate that normal advisors, so I'd actually guess about 5% of PhD advisors are a serious problem.
I will note that your experience will vary wildly based on gender and race. You are much more likely to find that inappropriate or abusive behavior from faculty as a woman, for example. It's hard to generalize because an advisor who is perfect for male students may be abusive to female or non-binary students.
That said, the abusive part of academia is smaller than the part that isn't abusive, but will apologize for it and gaslight victims into silence. That's the fraction I'd be more interested in quantifying.