Just think about this, if you go to gym, do some sport, crossfit, whatever, you'd know it is certainly impossible for a human being anywhere on the planet, to even run 200 mts. without oral breathing at some point. If you keep doing physical activity your body eventually would have gone through years of orals breathing just by doing regular physical activity.
You actually need to breath by the mouth to increase the air pumped to the lungs, without that you rapidly exhaust the nose capability and you can't perform beyond marginal movement, i.e. you can fastly walk, but you won't run for long just by breathing by your nose.
So it looks a lot like from the point of view of evolution, our bodies are precisely made to breath by the mouth for short periods, which eventually account for long periods, and hours, months or years in the long run.
So it looks a bit like oral breathing is an expected normal function of the body.
ok, it is not that is a perfect function, or that it will keep you healthy at a 100% of the attempts, but is - this is my take - probably that breathing by the mouth is one more body function, a standard one, evolved to be regularly used, with some trade-off, cost / benefits involved.
It looks like we are beginning to underping those tradeoffs, but it is actually almost impossible to live normally without using those functions.
An example could be using teeth, which leads to quite a lot of bad issues in the mouth and probably affect lungs, the hearth, and a lot more. But you can't just stop eating and oral hygiene goes so far, it won't fully prevent issues, eventually something is going to fail there.