I agree with you that one part of the solution is to stop hiring people who only know that culture. The ability of individual agents to sow dysfunction far outstrips any individual contributions, in my experience.
However, I'm not sure that diversity is really a solution so much as a symptom of a solution, which is a healthy professional culture. Adding women and POC may work tactically but it's not a great long term strategy for solving that particularly problem -- it's entirely possible for women and POC to behave in this manner (although it's quite a bit rarer in my experience). Not saying you're suggesting this, but I've seen quite a few orgs where women and POC are hired as tokens and don't get to real positions of power where they have the power and responsibility to truly run things and reform/refactor systems. Reforming your organization so that it's not toxic to women and POC is an indicator that you're not going in the wrong direction, but it's hardly the end goal. In fact, it should be positively mundane, boring, average and the norm (and hopefully, will become that way soon).
Will these problems cease at that point? I doubt it. Callous, abusive leaders exist everywhere, and short of a massive societal shift where nonviolent communication becomes required reading for managers and leaders (which is verbatim what Satya Nadella did at Microsoft to great effect), the high leverage move would be to start there and not paper over the root.
These problems come from the top -- corporate and engineering leadership. If you have a culture that accepts and allows for brilliant jerks, there are a couple root causes:
1) Your leadership aids and abets it
2) Your leadership is apathetic about it
3) Your leadership dislikes it but feels powerless to stop it
If you've got issue class 1 or 2, it's likely more pragmatic to leave than try to wage a cultural coup (of course, more power to you if you can pull that off). If you've got issue class 3, well, maybe you've got some options. You can convince leadership that they've got a certain kind of problem -- easy enough. Then you've got to convince leadership that a given approach could ameliorate it -- doable, but tricky and not at all a guaranteed success. Finally, you've got the hardest part: actually implementing it. The resulting shift in power could result in folks trying to sabotage things, and success will be doomed unless it is unilaterally supported and individually guided through by leadership. This is rare, but possible (again the Nadella reference). But again, the goal should be to create a cohesive, respectful, supportive teamwork oriented environment, and the means should support that.
If you can pull that off, achieving not just diversity but a safe, sustainable place for folks of diverse backgrounds to thrive becomes a real possibility. I think that's why it's worth setting our sights there in the first place.