MAD doctrine can't be applied in terms of the economies among China and USA, because they are different kind of societies and power structures.
USA is individualist, China power is based in Han Chinese ethnicity patriotism.
If USA elite interests are not affected, it doesnt matter what happens.
MAD doctrine in the military terms worked because USA elite lives were affected and under threat.
USA elite lives are not affected by tariffs or economic decline, just common American people.
USA is big enough to keep shrinking and keep same life standards for their ruling elite.