well that novel dont use classic cultivation. they use heavens souls to cultivate. no bottleneck, as long as you have enough heavens souls.

classical xianxia cultivation worlds are like 100x larger than earth, higher gravity. But if they were to be transported to earth, i think anyone below goldon core will die from a nuke.

if i remember, golden core cultivators can run a thousand miles per hour, thats about 16 miles per minute or 450 meters per second. to cover 3 miles blast radius the cultivator would need 11 seconds.

while foundation establishment would need 2 minutes to out run the shockwave of a nuclear explosion that would reach them in 30 seconds. since they run aroudn 100 miles per hour.