That is some stupid shit right there.Holy shit man listen to you. Go google "do airstones add oxygen to water." You will find a million websites telling you they don't including aquarium websites. It will prevent anaerobic bacteria from growing but it will not add oxygen to your water. At best it adds AIR to your water which isn't even pure oxygen, if you've ever used a CO2 controller it will tell you earth's air averages about 400ppm CO2. You can deny science all you want but you're also probably one of those old fools who thinks leaving the lights off 48 hours before harvest is somehow going to change thousands of years of evolution in the plant's biological process just because some old hippy said so.
You ever grow with an Under Current? I know the answer is no. If you have you'd know they grow amazingly fast and the reason they do is because the tumbling of the water in the return bucket, the same way a river crashes going down stream, is what dissolves oxygen into the water at all times.
Your hydroponics have never been better than the 6 mg/L oxygen it had coming out of the tap. You have no clue what it's like growing with high dissolved oxygen levels because you've never tried any other method than just having an air stone. And you try to make comments when you have ZERO experience in testing for yourself.
Why do you think you have to change the water out of your hydro bucket every 2 weeks fool? Because your water ran out of oxygen and the plant needs the oxygen to feed.