The comment about "not controlling for O2" is referring to the fact that the human body can't directly detect blood oxygen levels, and only infers them from blood CO2 levels. So if something's going wrong with the oxygen absorption process but the CO2 exhalation process is still fine, that would explain why patients have dangerously low blood oxygen but aren't panting or otherwise showing respiratory distress.

(Incidentally this is also why it's really dangerous to hyperventilate before free diving, because you can put your O2 / CO2 ratio out of whack which can cause you to black out without warning while under water.)

CO (carbon monoxide) poisoning happens the way it does for this reason: You don't feel lack of oxygen - you feel abundance of (uncleared) CO2. If you have too much CO, you lack oxygen but don't have too much CO2, you just feel sleepy/drowsy but suffocate and die unless you do something.

Whether the rest of OPs theory makes sense, I don't know - but this part is indeed factual AFAIK.

The virus appears to impair hematic function in the lungs. The oxygen builds up, and it is quite caustic. It creates what are called ground glass bodies. Since the oxygen is trapped in the lungs and does not move the blood very efficiently, you get hypoxia.

But there there was low levels of O2, wouldn't it mean low levels of CO2? Body doesn't have enough O2 to produce much of CO2, seems plausible for me.