You dont really want to give + to weak girls but i dont see why you still implied it... Its not just about stats but skills and abilities etc too. For instance most generic girls have 1 target skills that deals nearly same damage with multiple hitter premium girls, also you have a chance to get adelite and other generic girls freely + versions of them so, what you said was pointless.

As for the last part, most of us gonna get a full event+prem UR+ girl team anyway sooner or later, i wouldnt bother with francette who has crap stats and ability... Didnt saw any full UR+ teams include her anyway on dmm, so better to gib her + to an overpowered premium to make it even more useful.