If you write your own custom admin for some models or apps then you've either got to write it for all apps or users will have two inconsistant admin interfaces to deal with with a different UI and feature set between them.
So you decide write a custom CRUD for all apps including all those pesky 3rd party ones. To avoid all that boilerplate you write a few bits of code to introspect models and declaratively customize the interface.
Guess what. You've just reinvented contrib.admin with less features and more bugs.
Learning to customize the admin isn't hard and takes surprisingly little code.
In return you get a single consistant UI for all your code.
I see your point. I'm not against customization. If your admin site is used a lot, you don't really have other choice. However, customizations tend to pile up and become maintenance burden, so personally I prefer to strictly limit use cases for the admin site. Hence, problems listed in original post may signify that the admin site is overused, a higher-level problem that would need to be solved first.
If you write your own custom admin for some models or apps then you've either got to write it for all apps or users will have two inconsistant admin interfaces to deal with with a different UI and feature set between them.
So you decide write a custom CRUD for all apps including all those pesky 3rd party ones. To avoid all that boilerplate you write a few bits of code to introspect models and declaratively customize the interface.
Guess what. You've just reinvented contrib.admin with less features and more bugs.
Learning to customize the admin isn't hard and takes surprisingly little code.
In return you get a single consistant UI for all your code.