>>The US and NATO could trivially cripple Russia's army in the field.

The USA has not fought an symmetric war since WW2.

Russian has some of the most advanced surface to air missile technology in the world, capable of denying NATO air power from operating effectively. Russians S400 missiles can detect and take out even F35s. A direct air assault like you saw in 1990s Iraq war would be suicide.

You would be looking at defeating 100,000+ soldiers equipped with armored vehicles and tanks with primarily ground forces. This is not the kind of scenario we want to see.