ELT will not discover many new objects, it's built to do deeper followup observations of known targets. On the other hand, Vera Rubin was designed to be a survey telescope, repeatedly imaging the entire night sky to discover new objects. It will not do targeted observations, or at least very few.

>Vera Rubin was designed to be a survey telescope, repeatedly imaging the entire night sky to discover new objects.

The entire _southern hemisphere_ night sky right?

Yeah, not the entire northern sky at least. It's located only 30 degrees south though, so its coverage will be pretty damn good.