The same criticisim would still apply. There must have been many generations of squirls with flaps of skin big enough to get in the way, but not big enough to be useful.
A Discovery / BBC documentary once showed an experiment where they took this water-dwelling insect and cut its wings incrementally, to see for what minimum size they would remain useful.
Even on complete removal, just the flapping of the stumps was good enough for the insect to generate enough lift to bea able to skate over water with good speed.
You could try searching for that documentary. I’ll paste the link as soon as I find it.
Likewise for the squirrels, even a tiny bit of flap will increase the effects of drag, to allow the squirrel to survive higher falls than without them.
The smaller the creature, more pronounced is this aerodynamic effect.