1.) Namespacing XML is otherworldly.
I disagree. When your language is weakly typed, you're living in the past.
2.) Why bother with an envelope, which really provides no value, when your XML can be RESTful, such as:
<Login>
<Username>string</Username>
<Password>string</Password>
</Login>
The SOAP envelope is the single ancestor; it takes the place of your above "login" element. XML, strictly speaking, requires a single ancestor, so the argument is moot.
The purpose of the SOAP:body tag is to distinguish successful operation result message types from faults. I don't see how you can possibly argue that there's no value to it, when it's pretty clear what the value is just by looking at any example.