You haven't misunderstood the royal rota at all. It's been wildly mischaracterized by lots of people on social media - instigated - in my opinion - by statements made by Harry and Meghan on their exit website and interview comments.
The royal rota is simply a system of press passes for big or significant royal events and engagements to 'manage' the numbers of the press.
It's to prevent one organisation sending 20 people and another not getting the chance to send one photographer. It includes local media as well and helps local radio station reporters, or local newspaper staff being swamped with national press taking all the good spots (I was one of those local reporters - I still have my press badges from those events.)
And it's a sharing system for times when the event needs to be severely restricted to just one or two members of the press. In those situations the person chosen to 'be in the room' is not being given an exclusive but is required to release their photos, video, radio, and copy to be used by the whole pool.
For example the Queen's last official photo with Liz Truss.
The existence of the royal rota does not prevent members of the royal family giving exclusive interviews when they want to, to whichever media organisation or reporter they prefer. An example of this is when William chose to highlight the Big Issue and did the interview exclusively with the Big Issue.
The Sussexes were being disingenuous (or maybe they didn't understand the system themselves) when they implied that they were going to do a different kind of relationship with the press and only talk to grass roots reporters.
They were never in a position where they couldn't already do that.
It's only really significant state occasions that the royal rota is needed to make sure that coverage is fairly distributed across all the different media outlets. Everyone thinks of the main national tabloids but it's a system that includes multiple radio, TV and online journalists too, and local and regional press, and at times foreign press.
The rest of the time it's finding a way to contain and corral the huge media packs that turn up to the bigger engagements to keep everyone safe - royals, public, the press themselves. Some of those photographers have very sharp elbows when trying to get their perfect shots.