That's true.
I firmly believe the limits of Superman/girls/cat/dog are rooted in their minds.
I've seen Superman struggle to catch up with and stop a plane.
Then in the next instant he lifts mountains and fly across the earth in a second flat.
But as for Supergirl winning against WW, it's not a dead cert even though SG is so powerful.
You guys ever read Asterix comics?
In one, Obelix (who is invulnerable, superstrong, superfast) gets manhandled by a tiny little Chinese guy who knows kung fu.
Case in point.