(If I understand you correctly...)
The point it is not of it being lighter (most likely it won't) or more
compact (most likely it will). The point of the barn door tracker is
that it's easy to manufacture with commonly available materials and
parts. If you were to drive the swivelling platform directly you'd have
essentially a RA drive and that would require, in its turn, quite lot
more work and sophisticated parts, and likely access to a lathe as
well.

Andrea T.