Bottom-line, the air in a modern jetliner is fresh (enough!)
So indeed, with modern engines, the corporate penalty for clean cabin air is fuel consuption and power loss ( wrt Boeing article). The 50/50 mix is the norm but I'm sure this ratio can be 'confidentially' tweaked by company policy to reduce fuel burn.
Unless air quality is continuously monitored, to make it auditable, (quality parameters recorded along with other flight data) cabin air quality will continue to be poor in the interests of company operating costs.