An aftermarket fan could possibly work but not better than the original set-up, if it is in good working condition.
You said these cars do not show a very good design (air restriction). I don't quite agree.
If the car overheats in traffic, it is not because of poor design but it is due to some faulty coolant system components on your car.
I can let my car idle for hours in heavy traffic in a 100deg.+ heat, and it will never overheat.
If you decide to go with an aftermarket fan, it would be for economical reason, not to improve the original design.
JackD