Okay, so now we have the pictures. One rotor has some pitting, but
otherwise, there's not too much out of the ordinary from these rotors.
Yep, there is rusting on the wear surface. However that is indicative
that the pad is not resting flat against the rotor (as only about half
the surface of the rotor shows normal wear.) This suggests that the
pads on that side aren't sitting properly in the caliper on that side.
It could also be due to a bent caliper or (heaven forbid) an
incorrectly manufactured rotor (having one side not parallel to the
other). A micrometer measurement of the caliper would verify this last
quite quickly.

You haven't supplied a picture of the wear surface of the pads, or of
the piston. While there is plenty of meat on the pads, that's not
always important to properly functioning brakes. Correct assembly and
alignment of the parts is. The wear pattern strongly suggest that there
is an alignment issue on the piston side of your brakes (this could the
free floating caliper portion, but that side appears to have worn
properly, whereas the piston side has worn assymetrically.)