Also I'm not quite sure how Super GIRL tarnishes Super MAN's thing as the Last SON of Krypton.
Dilution of concept. At one point in the Silver Age, there was Superman, Supergirl, a Super dog, a Super cat, a whole bottle city of miniature Kryptonians (Kandor), and if memory serves even a Super horse
. (and that's not counting all the villains in the Phantom Zone).
It's hard to play the "last of my kind" trope when, frankly, you AREN'T "the last".