I use C-More Red Dot Sights and have never had one go out of zero after shooting hundreds of thousands of rounds. If you decide you are having too much trouble with your optics get a GREEN Fiber Optic and live with it. The green is the first color the eyes pick up and stays bright even in a low light indoor shooting range.
Last month I switched to irons for Steel Challenge and shot better than my optic average. That sight never moved and I was able to pick it up much faster.
BTW I've been shooting dots since the 70 and really believe in them. My first Vortex Venom had the same problem you describe. I sent it back in three times before I asked them to replace the sight with a Viper. No problems with the Viper on any of my guns.