In your opinion.... Not mine....
What exactly do you see making an aftermarket system better?
First, they are more compact, take up less space and weigh less. Second they are all electronic. Blend doors are operated by electric motors, not vacuum motors. The heater control valves are electronic, not cable operated. So they are more precise. Third the evaporator cores of todays air conditioners (R134 ) transfer more heat to the coil than the ( R12 ) evaporators.
Forth the condensers are designed to much more effectively eliminate the heat that was removed from the cabin of the car. And true, most block off the the cowl vent
But if I want outside air I'll turn the air off and open the window.