Now, if that Reseller needs to change something as fundamental as their own DNS records or hosting limits, they often find themselves locked out of their own management. Why? Because the reseller user is owned by the admin.
No that is totally not true. It's the same as with cPanel, give me an example of what a reseller can do in cpanel and can not in in DA.
Resellers can do as they want with their account. So they can also change DNS records, even their own. And hosting limits are set by the creator in any panel, either if it's root or admin totally doesn't matter.
Doesn't matter if they are sub user of system, root or admin, totally makes no difference as a reseller is never a main user.
As a reseller is never ever an admin on any panel (except in DA admin himself) there will always be restrictions, that's why it's reseller and not admin.
I still don't know where you get the idea that you would not be able to change your main domain as reseller because you can, even a user can. So that statement is not true at all.
Again, the issues you're pointing out now, are normally never to be seen and a warning is visible. So as said this must have to be related to something going wrong with CP to DA conversion. And conversions are in most systems never 100% perfectly.
This is not the place to discuss things which would not work, because it would spoil answers to the issue you are having now caused by the conversion.
If using a normal DA installation, I'm happy to proove to you that there are warnings and it's also logical that if you delete a reseller the whole tree (so everything below the reseller) is deleted to. And I've seen then warning before when deleting a reseller.
If I create a Reseller with domain.com, that Reseller cannot manage that primary domain's DNS or settings directly within their Reseller interface.
I have admin access but my company account is reseller and I don't know which DNS settings you can't change for the primary domain, because I can and I even use my own nameservers.

Check these things and make your statements after you have a correct working DA system and not one which is crippled due to a conversion issue.
As said I would gladly discuss this in off-topic or somewhere else, because you can close all you want but it's based on false statements.