Not to mention that they don't help stablizing all that much.
Take the P-38. This plane has noticeable flap effects. Enter a tight turn nearing the edge of stall, feel the plane wanting to stall, combat flaps down, and it stabilizes. Or, if someone wants to say that's because P-38s are Fowlers, then fine, although a little bit less in degree, the same with P-51 split flaps.
With the 109s, the flaps don't help that much at all. It's not that they don't have any effect in the turn radius, but rather it doesn't help in stabilizing the plane much. Feel a stall during a turn, put one flaps down.. nope.. not much difference. The plane still wobbles in the roll axis, and when that happens *sigh* stop input.. the speed builds, and then the flaps retract.
Basically, if you can't outturn a plane long enough to gain a gun solution without the use of flaps, then no amount of flaps are gonna help you - just don't use it at all. At least, I rarely use them in the 109.