Apologies, I specified "filtration" but meant "quality", which I would define as filtration + fresh air intake.

I'd have expected a better mix (more fresh air) since even with filtration removing many particulates and viruses, high CO2 levels still cause worse cognitive performance.

It's hard to get lots of fresh air into a pressurized plane, so I'm willing to have a good bit of leeway on that front. And airflow patterns are important; a lot of fresh air running from front to back would likely do more harm than good.