I was part of a hobby group that successfully addressed it's sexual harassment problem.  I wrote up my experiences here. 

I guess this does count as "lots of people leaving", as we kicked out the sexual harassers, and some of their friends left as well. This is why I don't think one should avoid conflict or people leaving at all costs: if you try to change the culture for the better, it's inevitable that some people who were comfortable with the status quo will take issue or leave. Of course, if you don't change, then a different set of people will be uncomfortable and leave or not join. It's a trade-off, and in the case of sexual harassers, a rather easy one. 

Changing the language they used

My dance group switched from gendered terms for the roles to non-gendered (blog post) and from calling one of the dance moves "Gypsy" to "right shoulder round" (blog post). This didn't involve strife in our specific community, though other dance communities had serious rifts over these two issues.

In the gendered terms case, our transition was the outcome of a long process with the community, including talking about various term options, trial dances, and then polling. We needed to do it this way because role terms are very visible.

In the "Gypsy" case the board and callers did it much more quietly. The caller booker told callers individually that we'd prefer "right shoulder round" if they were comfortable with it, then later that we strongly preferred it, and then eventually started asking callers not to use "Gypsy".

Communities where these two issues went poorly often had the people who were pushing for change taking a confrontational attitude, and accusing people who disagreed with them of being prejudiced. I think they typically also involved advocates pushing hard on this before the community was ready, not building support, and not getting buy-in from respected members.

One suggestion might be to look at Glassdoor or other company ratings and see how they change over time. While not being tracked for long, one might see e.g. DEI scores changing over time, perhaps a useful proxy for at least sexual harassment. Maybe not an answer but instead just pointing at where answers might be found.

EA forum posts used to be written much worse than they are now in terms of conciseness, clarity, and ease of understanding. I believe a series of posts came out mocking it / arguing against it, and shortly afterwards writing habits changed.