The answer is no I'm afraid. You still have to define your synthesis networks in the SuperCollider language and send them to scserver first. The library only "controls" the server, manages execution etc.

SuperCollider architecture works in this client-server system where a server can be controlled by osc commands. The server does also receive synth definitions via osc but there is no library for p5 that provides this functionality as far as I know. So you'll still have to define your synthesis networks from sclang, define appropriate parameters for them, and will execute/order/control them from processing.

You can write your synth definitions to use with your sketch "once" to disk and they will be controllable purely by p5 without requiring any supercollider application interaction forever, as long as the scserver is running. So if it is only "running standalone" you are caring for, that can be done by writing synthdefs to disk via calling .writeDefFile method on SynthDefs in SC and they will always be available. But if you are intending to use p5 as a substitute for sclang, that is not really possible (yet). There are mny many high level constructs in sclang that is aimed for music making and porting them all to another language would be hard.