I am by no means an aerodynamic expert but semi-symetrical wings generally perform much better inverted than flat bottom wings in my experience. This makes the plane perform outside maneuvers better. Symmetrical wings do even better yet.

I suppose it is true that flat bottom airfoils do produce more lift for a given surface area or they wouldn't be used so much on trainers. I don't think that tells the whole story though. Some semi-symetrical and fully symetrical wings provide a lot of lift and the planes glide very well. In some cases, almost trainer like. I assume this has to do with the specific characteristics of the airfoil, wing area, weight of the airplane (wing area and weight = wing loading), drag on the airplane, etc.

For example, a 4* and GP Rapture use a semi-symmetrical airfoil and the Tiger-2 is symetrical. In my experience, all glide well, land gently and don't have any "surprises". This tells me that the general shape of the airfoil is one factor but there are definitely others as well.

Like I said, I'm no expert though. This is based on what reading I have done and my own experience & observations.