My biggest problem making smarter "relays" is I'm limited to 5 pins. I think I can hold more stable temps with an electronic otterstat. PWM of the fans is going to make a lot of electrical noise and not gain much improvement. I made my fan relay hold 20 seconds just to stop the switching of fans on and off to reduce engine load changes at idle and improve the AC capability.

You defiantly don't want the fans to cool if the thermostat has not opened which is why (my guess) the otterstat was put in the outlet.

Fans have to run anyway when the AC is on which is most of the time in summer.