Since the first browser appeared I've always meant that sending a user agent id was a really bad idea. It breaks with the fundamental idea of the web protocol, that it's the server's responsibility to provide data and it's the client's responsibility to present it to the user. The server does not need to know anything about the client. Including user agent in this whole thing was a huge mistake as it allowed web site designers to code for specific quirks in browsers.
I can to some extent accept a capability list from the client, but I'm not so sure even that is necessary.
The User-Agent request-header field contains information about the
user agent originating the request. This is for statistical purposes,
the tracing of protocol violations, and automated recognition of user
agents for the sake of tailoring responses to avoid particular user
agent limitations.
What? Ideally it should just say "GET /path/to/page".
Sending a user agent is a bad idea. That shouldn't be happening at all, from any source.