In the Dream Domain, only the thresholds between layers would require a high complexity of one's mind, while what would change between layers, was the amount of power used to pressure the mental warriors who inhabited it.
That was the reason why Daniel, while not being able to walk past the threshold himself, was easily able to withstand the pressure of the second layer, which weighed on his mind at more than five times the power of the first one. If not for his cultivation, he would have already fallen to feelings of anxiousness, despair, and fear.
Aeron, on the other hand, was feeling the pressure differently. While not as complex as his own, the sheer power of the second layer was beyond his own level of cultivation, and in order to resist its pressure, he needed to put in a constant effort into defending himself.
This was not a waste of time for Aeron, who could use this pressure to nurture his own mind for as long as they stayed.