As an engr manager, I've often seen disparity as a result of being hired during good years vs bad years for the company. Or when someone gets a better offer to leave, the company may change their pay but no one else's. Or hiring externally vs a transfer from another internal team. Or whether the team is coding for frontend web vs dev tools, even if using the same language. Or if female.

It's always a challenge for one person to fix -- with HR, with the department head, with yearly budget. And sometimes fixing one disparity means not having the sway to fix another as well.

Which is to say -- pay transparency and unions are good for everyone. And if the company can't afford to treat the employees equitably, then the company shouldn't exist. (Or it should reduce its avocado toast budget.)