Resizing is something to be avoided when possible.
Only when up sampling.
If I make the QC render 720 wide (same aspect as 2000×800) and put this into a SD time-line the result is truly bad. If everybody followed your advice all films would be shot in SD. There would be no resizing right up to DVD. A 4k file still has end up on a SDDVD or Bluray/HDDVD
So in my tests a 2000×800 Quartz Composer movie in a SD time-line exports much much better than a 720×288 QC .mov
Much more detail. Gradients are smoother too.
Super-sampling is a concept where you make the render as big as possible so that when it is scaled and compressed there is much more information for the algorithm to work on. So you get a better result.