namespaces are absolutely a bear and always unpleasant to work with. The libraries to use xml are equally frustrating when you’re doing complicated things, unless you want to make a class for every single type of detail that this xml document wants - then it’s fine, but some of us don’t want to do that, or inherited a project that didn’t do that.
XPath is a struggle with namespaces, as well. It’s ... trying.
How is that relevant for config files though? If you implement an app and want to use a config file, you don't have to use namespaces. I agree that namespaces are no fun, so I don't use them for my config files.
Namespaces are great when used wisely: they allow for embedding unrelated XML fragments in your document and your application will not see them. Or versioning your XML in namespaces. XPath and namespaces are trivial but it depends on the library you use on how to setup the namespace resolving. My pet peeve about namespaces: people that use HTTP URLs for their declaration and expecting them to be resolved for some reason. The other one being people that see a namespace prefix and think that that is the actual namespace.
XPath is a struggle with namespaces, as well. It’s ... trying.