Wheel weight: Stop worrying about it. It doesn't make enough difference for you to feel.
These are not 1000 HP high performance machines. They are low speed, low performance, off road toys (and fun as sh*t).
Rotational Mass has to do with bringing the wheels up to speed "rotationally" not forward motion of the machine. The speed of your tires is so slow (26" tire = 775 Revolutions per mile), and your acceleration is so slow, that it is going to be imperceptible.
On the race track wheel weight is a tiny advantage you might play with. Not in the mud.
Your inability to spin tires in the mud is not related to the weight. It is a function of grip.
Additionally... Tire manufacturers usually reduce weight by reducing side wall thickness. I'll let you rationalize that.