You are right - I have noticed the same things.
I leave mine in Dynamic and just change the suspension as required.
I don't find the throttle snatchy in Dynamic mode around town, although if I was on a long highway trip, I would probably use road mode.
Rain mode softens the suspension even more and actually reduces the preload - you can feel the bike lowering slightly when you go to rain mode. Very useful for getting on and off ferries.
But, yes, what is seriously needed is a comprehensive, simple to read guide to the electronics/suspension on the XR.
The manual is hopelessly complicated - obviously written by a German engineer....