No. Just No.
Camping doesn't mean you are on the same position for 1 min, getting everything ready to attack.
Predicting retreat movement is piece of cake, play a map 2 times and you know the retreat path.
I don't get your first sentence. Fact is, that everything, that stands outside of that very defined target area, will barley get harmed by the barrage. Once you hear the thing firing (and you will hear it), all you need to do is shifting your units position and you wont suffer major casualties.
Knowing retreat paths is not the same as timig a barrage precisely to wipe retreating squads. Also people who blob and are thus more prone to mass retreat, are also more vulnerable to arty strikes killing their troops on retreat.
I played many games with and against the stuka and in my experience you can render the thing useless through good playing. It takes some effort and it's not always easy, but it's perfectly possible to avoid it's barrages.
. I could make one on Allied fanboys too so there isn't bias 
. Feel free to add whatever you think of. 
Relic Entertainment
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