I had the same feature on my 2008 X3 and love it. I was looking at a 4 Runner as a replacement before I really looked at the CX-5 and it really bummed me out that it didn't have it. Didn't even know the CX-5 had it until I went to turn on the wipers for the first time and was super happy to find the feature.
Maybe I've convinced myself that the system is more dynamic than it actually is, but I have found that turning on the auto function as soon as you *want* the wipers to work usually gives it a good baseline setting. So I will often bump the stalk to get one quick wipe and then as soon as I want the wipers, put it on auto and then it uses that amount of coverage over the sensor as it's baseline to activate the wipers. Then I can bump up the sensitivity if I feel like I need more. I have never needed to lower the sensitivity. But I could honestly have just made all of this up in my head. In two years of driving the X3, I never once had to use anything other than the auto setting. Same for the CX-5 so far, but that's only been a few months. both systems seem to work as well as each other.
It seems to me that if my assumptions of how the system work, leaving the stalk on auto all the time means that it would be hyper sensitive the moment it saw rain. Conversely, waiting until the windscreen is soaked and then moving it to auto means the sensor would be waiting to be completely covered again. This thread is going to make me google this now to figure out whether or not I'm insane.