I just care about them being fun. I know Scorpion is fun (though I would never play him in MK unless I randomed him) - as long as Zod and Batgirl are fun, I'm cool with them. Of course they have to be different too. I trust NRS. Sub-Zero and Cyber-Sub are both different. They made Kenshi and Ermac different. I trust them.
Wouldn't a FUN Red Tornado and Booster Gold be more fun though??
I'll admit those characters look cool and that I would prefer them. But I'm just basing that off of the way they look and what I've read on wiki pages - I'm not a DC fan, so I guess I'm not the right person to ask... but that kind of stuff fades off for me in fighting games anyways. What remains is how fun a character is to play, and how well designed their moveset is. Previous to MK9 I always considered Reptile my main, but Sub-Zero's redesigned moveset was so amazingly fun for me that now I'm a Sub main. I still think Reptile looks amazing, but Sub-Zero's playstyle just really clicked with me. You are right, those characters would be better, but at the end of the day the most important thing for me is always a well designed moveset.