I like to look at what I think are more authentic, indirect indicators, even though very imperfect, too.

For startups specifically, I used to analyze the startups that VCs tweeted the most. Uber dominated for a long time. And Zenefits was tops too, until they dropped fast in mentions a few weeks before their turn of fortune. Yeah, some tea leaf reading and eye of newt stuff, but interesting nonetheless and some job seekers found it helpful.

Your point about departing/departed employees and hellscape made me think about how the recent negative news about Google contrasts with one indicator (again, imperfect) of how happy people are to be Nooglers and Googlers -- their public exultation in Instagram posts: https://gxjam.com/ig-gallery/noogler-instagrams-by-googlers-...

Edit: Of course, neither of the above approaches are as broadly applicable as Glassdoor's approach