Nah, requiring Symfony is like requiring Django. Doesn't make much sense.
The irony is that for this very project, Both Silex and Symfony\Process are completely redundant, especially with PHP bloated core APIs.
The only other required libraries for Silex to function are the event dispatcher, routing (which you can swap out for something like nikic/FastRoute), and the request/response stuff. I'm not sure if you think that's a "lot" of code, but if you're rolling your own you'd probably end up using the HTTPFoundation stuff anyway.
That's exactly what I said, what is the point of your message? With Silex there is no configuration through XML or YAML. What is not correct?
Event dispatching + kernel (basically a handler) + request/response isn't particularly complex, is it?