The easier solution would be just to reduce the amount of fastpasses given out. I don't care if it would make them harder to get.
Either that or lower the ratio. I get that FP+ is supposed to shorten waits, but all it really does is let you get on three things fairly quickly at the expensive of significantly increasing standby wait times at every other attraction. I'd argue that without FP+ in place at all, people's overall average waits would go down quite a bit and visitor satisfaction would be higher. At ticketed events like MNSSHP (which are still very crowded), there are no fastpasses in use, and the standby lines move very quickly, even for popular rides like Splash Mountain.