Let me add...
I mentioned a lot of this is about me liking cool stuff and seeing what works best, event though I'm doing this for my kid.
So I'm looking at a light 20.5 mm setup with 33mm wide mud tires.
Something is wrong/mis-matched with that I think. If the wheels are caked with mud and the speeds are slow, what is the point of saving a few grams?
If things are dry, the light weight matters more, but thin rims squirm more than thicker ones.