As far as I can tell the rule is simple: If you are not expected to speak in the meeting, your camera should be off; otherwise your camera should be on the entire meeting.
Also, what is the value in having it on? I've worked places where they want your cameras on during all staff meetings with 100+ people on them. I don't actually understand the upside to having it on.
If leadership wants to have their own cameras on because they feel it conveys intent and emotion better when I can see their face... that sounds like they made a decision. Leaders often have to lead with emotion so wanting to convey emotion better might be a good choice for them. Most of the meetings I'm in are about facts. And I dont feel like I need facial expressions to express data more effectively.
Anyone who worked pre-Zoom for a large corporation with offices spanning multiple cities will remember having conference calls simply because everyone was in office, but there were 2-3 offices to connect together. And you could see people in your own office, but you couldn't see people in other offices, and not being able to see people was never an issue back then. This isn't even a new concept. It worked for DECADES just fine.
The other company is strictly no cameras. I love it. I don't think I've had one meeting where anyone had their cameras on.