How to prevent half wall (drywall, steel studs) from wobbling
Residential steel studs aren't rigid on their own. They get rigidity from the surfaces they are connected to along with the drywall that is attached.

For a wall like that, I'd want to treat it like a newel post on the end and have it be a 4x4 blocked and bolted to the joist below it for rigidity. 

Otherwise, your idea to just make it a full column would work too.