I get a headache if I wear VR glasses for a few hours or if I watch TV for too long (and I don't get headaches normally). But I'm pretty sure neither is affecting my oxygen/CO2 levels.
In other words, headaches != oxygen starvation. If medical personnel were being oxygen starved due to PPE, doesn't it make sense that they would notice that pretty quickly in a place that's literally full of oxygen sensors? I've noticed that many doctors are quite paranoid about their health, and you can bet that some number of them have been checking their blood oxygen levels.
Nor does a mask create a petri dish. You're supposed to replace them anyways (or wash them if you're using a cloth mask). But during the time of the normal wearing of a mask, the germs such as they are there are going to be coming mostly from your body, which is apparently equipped to handle whatever is there.
Hospital masks have been worn by doctors for ages, and no one was accusing hospital administrators of some huge conspiracy to control surgeons, even though they are required to mask up before a surgery. Yes, they "have " to do it, but it's for a very practical reason. Would you prefer that medical personnel were "free" to operate on you without wearing protective gear and washing their hands first?
And it's not like forcing someone to wear a mask controls them in other ways. Robbers are "forced" to wear a mask when robbing a store to avoid getting caught. Was the robber controlled or made docile by the mask? Most stores would say no.