This. Like when marvel want to cast agent coulson for the tv network. They use the same actor. So the sense of coherence is there.

Dc is not having a proper planning.

Plus, i dont like the supergirl actress. Imho her smile is annoying, and her shoulder is too broad. I am not condemning her physical, i am just expressing my disagreement with the casting choice made by the casting director. Off the top of my head I can think of a lot of actress that would have a better look to be Supergirl.