I never trust surveys of companies even if it is a reputable 3rd party. There are too many ways to game such systems. If I wanted real answers I would find out who works in the group(s) I might end up in and reach out to them via email if I can and then set up a call. I would be honest and say I do not trust surveys of "best places to work" and would happily sign an NDA to not share their brutally honest answers. Even that I would take with a grain of salt as they may think it is a test or trap.
Convincing current employees may work on those that are isolated but if one works in a toxic environment they will likely know it. There was a time I would have semi-trusted sites like f'd company of long ago but those get infiltrated, sued and ultimately compromised by corporations that do not like people airing their dirty laundry and also gamified by their competitors.
If a new position turns out to be a crap-show I would just leave and not add it to my CV. If an individual manager is the issue, those come and go. I have found it very easy to make them explore new opportunities.